Overview
========
This PR implements the view change and recovery portion of IR. It also
fixes a couple of important bugs and introduces a new mechanism with
with to unit test IR.

What's New?
===========
This PR includes the following, in roughly descending order of
importance:

- The main contribution of this PR is the implementation of view changes
  and recovery. The implementation required some of the following
  things:
    - I introduce DoViewChangeMessage and StartViewMessage protobufs as
      well as protobufs for serializing records.
    - IR replicas have logic to periodically initiate a view change or
      initiate a view change upon recovery. They also have logic to
      handle DoViewChangeMessage and StartViewMessage messages.
    - IR replicas persist their view information, which is needed for
      recovery, using PeristentRegisters which persist data on disk.
    - When a client issues a PropseInconsistentMessage or
      ProposeConsi...