changed test to check if leader can respond with cluster's config
WIP making any cluster membership change go via the JoinedConsensusStep
Election and adding nodes now works as expected
Need more tests around the leader going away

TODO the actual "joined consensus voting" is missing, adding it now.

refs #9
[#9] massive changes, introducing JoinedConsensus ready membership
changes; Removed old "add member" and "remove member" messages,
which could have led to many Leaders selecting themselfes