PaxosRole doesn't model the low-ball prepare state

[simbo1905]

PaxosRole currently has three states, Follower, Recoverer and Leader. The logic actually has two states for a Follower, one which is normal running and the other which is when it has timedout and issued a lowball prepare. It would better document the actual state machine if we modelled awaiting the responses to the lowball prepare as a different state. That could be something like Candidate to indicate that it is seeking to be the leader.

[simbo1905]

Whilst we are at it the term Role might be applied to the concept of proposer, accepter and learner. So we might consider renaming it to be PaxosState.