Refactor GetBlockVerboseTx to reflect correct getblock RPC call parameters.

[jalavosus]

Currently, rpcclient.GetBlockVerboseTx(...) does not return raw transaction data. This is due to how GetBlockCmd is implemented in btcjson; in upstream/master, getblock sends two boolean parameters (verbose and verbosetx), which throws an error.

According to the bitcoin JSON RPC documentation, getblock accepts two parameters: blockhash (as a string) and verbosity (as an integer). verbosity can be any of 0, 1, or 2, with 0 being the default.

getblock "blockhash" ( verbosity ) 

If verbosity is 0, returns a string that is serialized, hex-encoded data for block 'hash'.
If verbosity is 1, returns an Object with information about block .
If verbosity is 2, returns an Object with information about block  and information about each transaction. 

Arguments:
1. "blockhash"          (string, required) The block hash
2. verbosity              (numeric, optional, default=1) 0 for hex encoded data, 1 for a json object, and 2 for json object with transaction data

This pull request aims to correctly implement verbosity as a parameter to getblock by refactoring GetBlockCmd (in btcjson/chainsvrcmds.go) to have two fields: Hash and Verbosity, with Verbosity being an optional int pointer.

In order to implement correct behavior, three primary changes are necessary: the above refactor, an additional type specific to getblock verbosity=2, and a new Future type to enable proper (and error-free) unmarshalling of verbosity=2 data.

The new type (GetBlockVerboseTxResult) is almost entirely the same as GetBlockVerboseResult, but with the minor modification of changing the Tx field from a []string to a []TxRawResult so as to enable proper unmarshalling.

The new Future type (FutureGetBlockVerboseTxResult) returns a GetBlockVerboseTxResult rather than a GetBlockVerboseResult so that data can be properly returned to the user without error.

[jalavosus]

Additional data from the RPC documentation:

Result (for verbosity = 0):
"data"             (string) A string that is serialized, hex-encoded data for block 'hash'.

Result (for verbosity = 1):
{
  "hash" : "hash",     (string) the block hash (same as provided)
  "confirmations" : n,   (numeric) The number of confirmations, or -1 if the block is not on the main chain
  "size" : n,            (numeric) The block size
  "strippedsize" : n,    (numeric) The block size excluding witness data
  "weight" : n           (numeric) The block weight as defined in BIP 141
  "height" : n,          (numeric) The block height or index
  "version" : n,         (numeric) The block version
  "versionHex" : "00000000", (string) The block version formatted in hexadecimal
  "merkleroot" : "xxxx", (string) The merkle root
  "tx" : [               (array of string) The transaction ids
     "transactionid"     (string) The transaction id
     ,...
  ],
  "time" : ttt,          (numeric) The block time in seconds since epoch (Jan 1 1970 GMT)
  "mediantime" : ttt,    (numeric) The median block time in seconds since epoch (Jan 1 1970 GMT)
  "nonce" : n,           (numeric) The nonce
  "bits" : "1d00ffff", (string) The bits
  "difficulty" : x.xxx,  (numeric) The difficulty
  "chainwork" : "xxxx",  (string) Expected number of hashes required to produce the chain up to this block (in hex)
  "nTx" : n,             (numeric) The number of transactions in the block.
  "previousblockhash" : "hash",  (string) The hash of the previous block
  "nextblockhash" : "hash"       (string) The hash of the next block
}

Result (for verbosity = 2):
{
  ...,                     Same output as verbosity = 1.
  "tx" : [               (array of Objects) The transactions in the format of the getrawtransaction RPC. Different from verbosity = 1 "tx" result.
         ,...
  ],
  ,...                     Same output as verbosity = 1.
}

[jalavosus]

Closing due to incorrect branching