Task 2.1.2: Implement Zcash RPC functionality required by lightwallet services.

[idky137]

Implement Zcash RPC functionality required by lightwallet services.
This should be implemented as methods on StateService with identical functionality to the following Zcash RPCs:

• [getinfo]
• [getblockchaininfo]
• [getaddressbalance]
• [send_raw_transaction]
• [getblock]
• [getrawmempool]
• [z_gettreestate]
• [z_getsubtreesbyindex]
• [get_raw_transaction]
• [getaddresstxids]
• [getaddressutxos]

The following RPCs will be completed in #59:

• getaddressdeltas

• getaddressutxos

• getblockcount

• getblockdeltas

• getblockhash

• getblockhashes

• getblockheader

• getchaintips

• getdifficulty

• getmempoolinfo

• getspentinfo

• gettxout

• gettxoutsetinfo

• z_gettreestate

• getmininginfo

• getnetworksolps

• getnetworkinfo

• getpeerinfo

• ping

• Blocked on Task 2.1.1: Create StateService struct in Zaino-State, initially containing Zebra's ReadStateService, and implement sync method (using Zebra's TrustedChainSync) as a persistent background process. #110

[AloeareV]

send_raw_transaction needs to interface with the mempool, I think this puts it in the scope of #118 and not this issue? I think there are other mempool-related ones (getrawmempool I assume) but that's the first one I've hit.