+act #15383 add strict japi.Option.getOrElse to simplify working with options from Java

(cherry picked from commit 657afbd8591b28c1aef137520479d789bdfae83d)
Merge pull request #15432 from spray/w/add-japi-Option-getOrElse-backport-to-2.3

+act #15383 add strict japi.Option.getOrElse to simplify working with options from Java (backport)
=per #15429 Rewrite persistence documentation and samples for 2.3.4 changes
Merge pull request #15443 from akka/wip-15429-persistence-docs-patriknw

=per #15429 Rewrite persistence documentation and samples for 2.3.4 changes
+per #15327 Add AtLeastOnceDelivery trait

* also remove final of around methods, and let deliver send when not recoveryRunning