Add: account query database

[Frank-AFN]

Change Description

Add account query db, link to EOSIO feature. resolve: #159

Consensus Changes

API Changes

$ curl http://127.0.0.1:8888/v1/chain/get_accounts_by_authorizers -d '{"keys":["EOS..."]}' 2>/dev/null | jq '[.accounts[].account_name] | unique'

$ curl http://127.0.0.1:8888/v1/chain/get_accounts_by_authorizers -d '{"accounts":["alice"]}' 2>/dev/null | jq '[.accounts[].account_name] | unique'

Documentation Additions

--enable-account-queries

default: false

Boolean that indicates whether the Account Query DB should be initialized at start-up and maintained for the life of this instance. if set to true then the RPC endpoint for /v1/chain/get_accounts_by_authorizers will be registered otherwise it will not be present and requests to that endpoint will return 404 errors.