+act #13992 Improve identify replies of wildcard selections

(cherry picked from commit 4747b18d66fafb5699168288b09b7f39da5c2e4e)

Conflicts:
	akka-actor/src/main/scala/akka/actor/ActorSelection.scala
	project/AkkaBuild.scala
Merge pull request #15421 from akka/wip-13992-identify-wildcards-master-patriknw

+act #13992 Improve identify replies of wildcard selections (for validation)
preparation for asynchronous DNS resolution
fixes after review, including: better .conf organization, dynamicAccess instead of Class.forName, immutable Seq's