Tracking: Fully support mining usecase

[mpguerra]

Motivation

In order to enable zcashd deprecation, we need to ensure that solo miners and mining pools are able to use the new zebra stack instead of zcashd.

For this to happen, we will need to implement and update a number of RPC methods. The child issues listed so far are non-exhaustive and we may add new RPC methods as new information arises.