Refined doFollow and onAppendEntries, so all the work of appending / committing happens inside the RPC call
Separate out leader and follow responses to an AppendEntries request, for simplicity...and for a guarantee that there is no race condition between appends / commits in one thread affecting another. Leaders *only* append and commit in their doPerform thread; followers *only* append and commit their doFollow thread.
Shared code between doFollow/doRespond.