+per #15424 Added PersistentView, deprecated View

A PersistentView works the same way as View did previously, except:

* it requires an `peristenceId` (no default is provided)
* messages given to `receive` are NOT wrapped in Persistent()

https://github.com/akka/akka/issues/15424
good, also mention something about how to define old path based id (to be able to continue reading old data)

    self.path.toStringWithoutAddress