!con #3597 Remove hand over data message in cluster singleton
=clu #3608 Simplify Reachability merge

* No need to merge the individual rows for one observer, simply pick
  the rows from the observer with highest version
=clu #3533 Harden cluster startup error handling
Merge pull request #1719 from akka/wip-3597-cluster-singleton-hand-over-patriknw

!con #3597 Remove hand over data message in cluster singleton
Merge pull request #1740 from akka/wip-3608-simplify-merge-reachability-patriknw

=clu #3608 Simplify Reachability merge
Merge pull request #1741 from akka/wip-3533-cluster-startup-failure-patriknw

=clu #3533 Harden cluster startup error handling