Implement IBC contract support

[alpe]

Integrates IBC support for Wasm contracts. 🎉

Entry points

Wasm contracts can implement the following entry points to become an IBC port assigned automatically: wasm.<contract-address>

Channel lifecycle

A contract can receive/send packets via channels.
See IBC flow

Handshake start: OnChanOpenInit, OnChanOpenTry,

• pub fn ibc_channel_open

Handshake confirmation: OnChanOpenAck, OnChanOpenConfirm

• pub fn ibc_channel_connect

Close: OnChanCloseInit, OnChanCloseConfirm

• pub fn ibc_channel_close

Packet lifecycle

Packets transport data on the application level. See [IBC flow](https://github.com/cosmos/ics/tree/master/spec/ics-004-channel-and-packet-semantics#packet-flow--handling]

• pub fn ibc_packet_receive

• pub fn ibc_packet_ack

• pub fn ibc_packet_timeout(

New IBC messages

• TransferMsg - start an ICS-20 transfer using the cosmos-sdk IBC/transfer module
• SendPacket - send an IBC data package on an existing channel
• CloseChannelMsg - initiate close procedure for an existing IBC channel

Credits

This PR contains also a lot of work and feedback from @ethanfrey and @webmaster128 👏

[codecov]

Codecov Report

Merging #394 (edad9ef) into master (e6735eb) will decrease coverage by 0.87%.
The diff coverage is 48.58%.

@@            Coverage Diff             @@
##           master     #394      +/-   ##
==========================================
- Coverage   56.13%   55.26%   -0.88%     
==========================================
  Files          34       39       +5     
  Lines        3461     4015     +554     
==========================================
+ Hits         1943     2219     +276     
- Misses       1373     1617     +244     
- Partials      145      179      +34     

Impacted Files	Coverage Δ
app/test_access.go	0.00% <0.00%> (ø)
app/test_helpers.go	0.50% <0.00%> (-12.00%)	⬇️
x/wasm/internal/keeper/options.go	0.00% <0.00%> (ø)
x/wasm/internal/types/codec.go	41.17% <0.00%> (-2.58%)	⬇️
x/wasm/internal/types/tx.go	49.09% <0.00%> (-4.91%)	⬇️
x/wasm/internal/types/types.go	23.93% <ø> (ø)
x/wasm/ibc.go	59.37% <59.37%> (ø)
x/wasm/internal/keeper/handler_plugin.go	78.26% <74.64%> (+2.03%)	⬆️
x/wasm/internal/keeper/ibc.go	75.00% <75.00%> (ø)
x/wasm/internal/keeper/keeper.go	88.64% <77.55%> (-1.92%)	⬇️
... and 9 more

[ethanfrey]

Great (team)work here!

One minor nit, then let's merge this. And extend the functionality with more PRs to come.

Also: should we make a note on the README that master is not to be used except local tests? We are based on git commits of wasmvm and cosmwasm, and interfaces are in flux.

[alpe]

Also: should we make a note on the README that master is not to be used except local tests? We are based on git commits of wasmvm and cosmwasm, and interfaces are in flux.

This has not changed afaik. Anything before v1.0.0 should not be considered stable.
https://github.com/CosmWasm/wasmd#stability