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