Add cross-building client support for scala 2.11.

* Bump play version to 2.3.0-RC1
* Cross publish the client source code with Scala 2.11
* Remove akka/garbage from integration tests and versioning.
Ensure cient-all is also cross published for 2.11
Merge pull request #129 from sbt/wip/cross-publish-211

Add cross-building client support for scala 2.11.