Create getblock endpoint

[lijianl]

some API in module Blockchain is not available to use? and bchjs can not support to scan block transaction

such as

1. getblock
   2, getblockDetail(list transactions od block)

[christroutner]

The getblock RPC call is not implemented in bch-api. That feature request has been captured in this Issue. If that feature is added to bch-api, then an endpoint can be added to bch-js.