Upgrade Akka to 2.3.0-RC1

- Upgrade Akka to 2.3.0-RC1
- [Add parens to `sender` reference as recommended]
  (http://doc.akka.io/docs/akka/2.3.0-RC1/project/migration-guide-2.2.x-2.3.x.html#Parens_Added_to_sender)
Fix removed or deprecated Akka Java API
Merge pull request #2288 from guersam/tmp/akka-2.3

Upgrade Akka to 2.3.0-RC1