+per #3927 Enable EventsourcedProcessor to handle ConfirmablePersistent

(cherry picked from commit 6db2a2838a142798a97889486712bfd0f9f5052e)
=per #3957 Always reject external Persistent in EventsourcedProcessor

(cherry picked from commit 229578b559b302f0873e16385ba28ab3dabd9035)
Merge pull request #2121 from akka/wip-3957-EventsourcedProcessor-reject-Persistent-master-patriknw

Forward port of #3927 and #3957