Add 'witness_v1_taproot' script type to the enum and proto.pb, so that
it doesn't cause any problems when Taproot is activated and the new
script type starts showing up in RPC getBlock(..) responses (including
possibly BSQ transactions).

Also change the Java enum order (which shouldn't cause any problems as
the ordinal isn't used directly in hashCode calculations) and add the
missing 'witness_unknown' enum value to pb.proto to bring it in sync.

Create a new 'BitcoindClient' interface and a corresponding builder, to
replace the old 'com.neemre.btcdcli4j.core.client.BtcdClientImpl' class
from the btcdcli4j library. This is instantiated by jsonrpc4j using a
dynamic proxy. It provides only a cut down version of the bitcoind RPC
API, exposing the methods 'getblock', 'getblockcount' & 'getblockhash',
as they are the only ones currently being used by RpcService.

Add corresponding Jackson-annotated DTO classes to model the JSON
structures returned by bitcoind, very similar to the classes provided by
btcdcli4j. Note that we use Double instead of BigDecimal to represent
fractional fields (difficulties + coin amounts in BTC), as they have
more consistent Jackson (de)serialisation and appear to be able to
faithfully round-trip numeric fields produced by bitcoind. Also note
that doubles can faithfully represent any valid decimal BTC amount (that
is, with 8 d.p. of precision) up to 21 million.

For now, keep the old BtcdClientImpl instance used by RpcService in
place, as the btcdcli4j block notification daemon is dependent upon it
and would also need to be replaced.

Also add unit tests for BitcoindClient which test against sample regtest
responses, using a mock HttpURLConnection.

Provide a new 'BitcoindDaemon' block notification socket server, to
replace 'com.neemre.btcdcli4j.daemon.BtcdDaemonImpl'. This starts a
single service thread to listen for raw block hashes on localhost port
512*, sent by the specified 'blocknotify' shell/batch script, delegating
to a pool of worker threads to run the supplied BlockListener handler.
Unlike the original BtcdDaemonImpl class, a call to the 'getblock' RPC
method is not made automatically to supply a complete block to the
handler, instead requiring a separate, manual BitcoindClient.getBlock
invocation from within RpcService.

Also provide unit tests using a mock ServerSocket + Socket.

TODO: Use the new Bitcoind(Client|Daemon) implementations in RpcService,
 in place of btcdcli4j Btcd(Client|Daemon)Impl & remove the old library.

Wrap any exception that occurs during socket IO or within the supplied
BlockListener with a new 'BlockNotificationException'. This brings the
exception handling more in line with that of the old BtcdDaemonImpl and
makes it easier to match them downstream in FullNode.handleError.

Migrate RpcService over to the new block notification daemon and RPC
client based on jsonrpc4j. Drop in own DTO classes in place of the ones
defined by btcd-cli4j and rename requestBtcBlock & addNewBtcBlockHandler
to requestDtoBlock & addNewDtoBlockHandler respectively.

Also remove now redundant filtering from the logback config and update
grade-witness.

Factor out a new RpcService.extractPubKeyAsHex method, to take public
keys from the inputs of the raw transactions returned by the RPC client,
when building TxInput objects to incorporate into the DAO state. Enhance
the method to additionally support segwit (P2WPKH & P2SH-P2WPKH) inputs
(but only the first input for backwards compatibility - see code
comment). Also fix a bug when handling non-SIGHASH_ALL input signatures.

This will allow segwit BSQ to be used in proof-of-burn and issuance txs,
which need a public key associated with the tx to establish ownership of
it, when signing messages with a proof-of-burn or staking merit awarded
from a compensation issuance, respectively.

Also add unit tests for the factored-out method and add a missing RawTx
toString() method, to aid debugging the TxInput fields within the
processed block returned by RpcService.

Factor out shared construction logic to a new 'getBlockFromRawDtoBlock'
method in RpcService. Also add some 'NOPMD' comments in an attempt to
suppress unfixable Codacy warnings about qualified imports.

Prevent intermittent test failures, caused by a race between checking
whether the mock socket is closed upon accepting a new connection and
setting 'socketClosed' to true during shutdown. Waiting to accept and
then checking the flag needs to be done in a synchronized block.

Selectively disable pubkey extraction from segwit inputs of a particular
tx at block height 660384 (2020-12-07), which spends spuriously created
segwit BSQ (later burned), to prevent a change in the DAO state hashes
from that point.

(Since a tx with a given ID can only appear on one chain, a fixed global
exclusion list of IDs should not cause any issues on testnet/regtest
versus mainnet. This is simpler than conditioning by block height.)

Provide a 'NetworkInfo' DTO class (with associated nested DTO classes),
returned by the 'getnetworkinfo' RPC method call to bitcoind. This will
be used during startup of RpcService to determine if Bitcoin Core is
available and which version it is using. Add a unit test to round-trip a
sample NetworkInfo JSON response.

Also add the missing 'getbestblockhash' RPC method, which will be needed
by RpcService to determine the Bitcoin Core node health.

Make a 'getnetworkinfo' RPC call to bitcoind immediately upon startup,
to check that the node is up (and throw a ConnectException to ensure
that the user is presented with an appropriate warning popup otherwise).
Log a warning if the node version is outside the 0.18.0 - 0.20.1 range.

Additionally, call 'getbestblockhash' to check that the chain tip is not
stale (> 6 hours old). As part of this, make sure the 'getblock' RPC
call works correctly with verbosity < 2, by fixing JSON deserialisation
of the response when the block or txs are in summary (hex string) form.

(These version & health checks are almost identical to the ones done by
the original btcd-cli4j library during RPC client startup.)

Since extraction of segwit pubkeys technically represents a hard fork,
activate it by block height in the same way as the fork defined in
TxOutputParser, instead of relying on the absence of premature segwit
BSQ inputs outside of a blacklist. This also means we no longer need to
exclude all but the first tx input from segwit pubkey extraction to
maintain backwards compatibility, which is a little safer and consistent
with the original behaviour of extracting every available P2PKH pubkey.

Provisionally activate this (2nd) DAO hard fork at block height 672646,
which should be 6 weeks from now, just under 5 weeks from the planned
1.5.5 release on 2021/01/27. (Block 1906689 for testnet - 2 weeks from
now assuming an average block time of 10 minutes, but it's erratic.)

Add missing 'connections_(in|out)' JSON properties to NetworkInfo that
came with the recent 0.21.0 release of Bitcoin Core. Also ensure that
unrecognised JSON properties are ignored, so that future changes to the
RPC API are less likely to break our client.

Also, for the benefit of the tests, change the JSON property order of
RawInput to better match observed 'getblock' responses. (It appears that
in 0.21.0, extra "txinwitness" fields have started appearing in coinbase
inputs, which may be a bug.)

Avoid name clashes between the Json RPC client DTOs & the corresponding
raw (un-parsed) DAO state entities. Also prepend the other DTO classes
with 'Dto' for consistency.

Change jsonrpc4j version from 1.5.3 to 1.6.0.bisq.1, forked to the Bisq
repo from the recent 1.6.0 release. The forked version changes the class
'com.googlecode.jsonrpc4j.HttpException' to be public, instead of (prob.
mistakenly) package private, so we can avoid using reflection to catch
it and re-throw as a 'bisq.network.http.HttpException'. Remove the now
unused constructors from the latter.

As part of this, upgrade Jackson to the latest stable (2.12.1) release,
since jsonrpc4j now depends on a newer version than the previous 2.8.10.

Push back the (2nd) DAO hard fork activation block height to 680300,
which is 4 weeks after the planned 1.6.0 release around 2021/03/25.
(Also push back the testnet block activation height to 1943000 - 2 weeks
from now assuming an average block time of 10 minutes.)