1.6 - Outline of the Indexer design, contextualised by implementation

[idky137]

Finalise Zaino's design and spec.

This should be in the form of a set of design docs specifying both the internal design of Zaino and its API's. This should detail both use cases, as a live service and as a library. This should be added to Zaino's Docs folder.

• Blocked on 1.2 - Explicitly mark and broadcast list of lightwallet gRPCs to be deprecated #49, Task 4 of 1.5 - Implement lightwalletd gRPC functionality in Rust using JSONRPC interface for backwards compatibility. #52

NOTE: Due to ongoing conversions regarding the exact form of the extended remote functionality for the "cli-wallet" ("full node" API wallet), the exact spec for the services provided here will not be finalised until discussions are concluded in milestone 2 (#57).