=rem #13960 #13989 #13742 #13985  Optimize EndpointWriter

* Replace stash with internal bufferi, j.u.LinkedList
* Replace FSM with become
* Adaptive backoff, important to backoff, but not for too long,
  depends on environment and use case
* Prioritize heartbeat messages from remote watcher and cluster
  failure detector
* Use payload messages as heartbeats for transport failure detector,
  change transport failure detector to be based on absolute timeout,
  see ticket #13989 and #13742
* Log remote disassociate from transport failure detector,
  see ticket #13985
* Add benchmark sample in akka-sample-remote-scala
=sam Update Scala dependencies to 2.10.4
Merge pull request #2116 from akka/wip-3960-EndpointWriter-stashing-master-patriknw

=rem #13960 #13989 #13742 #13985  Optimize EndpointWriter
Merge pull request #15058 from akka/wip-update-scala-dependencies-for-samples-master-ban

=sam Update Scala dependencies to 2.10.4
build #15021,#13755 Emit statsd events during build
Merge pull request #15060 from ktoso/wip-15021-measure-each-test-perf-ktoso

build #15021,#13755 Emit statsd events during build
=pro #15031 use sbt-unidoc plugin