Nym 2.0

[idky137]

Refactor of the Nym code implementation in Zingo-Proxy. These changes are required to enable mutiple request types (RPCs) to be sent and received over the mixnet and to allow integration with Zingo-Proxy's request queue [WIP]. The walletside code is also refactored to ease wallet integration.

• Adds walletrpc, production ready walletside nym code implemented on librustzcash's CompactTxStreamerClient.
• Refactor NymServer, both to enable multiple request types and to enable integration with Zingo-Proxy's request queue.
• Implement get_info lightwallet RPC over nym, along with non streaming RPCs required to obfuscate client syncing.

Closes #14, #17, #18

[idky137]

Built on top of add_jsonrpc [#26]. Commits prior to this comment are from that PR.