Conflict Resolution phase should be non-blocking and restart on node failures

Currently if a node crashes during the conflict resolution phase, all topology updates and rebalancing is blocked until CR times out. As the CR timeout is the state transfer timeout, this means the cluster is in limbo for 4 minutes by default. This blocking behaviour occurs because currently the entire CR phase is executed in the merge thread, however it should occur asynchronously in a similar manner to a cache rebalance with CR restarting in the event of nodes leaving.