Upgrade of Activator to Play 2.3.0-RC1 (Akka 2.3.2, sbt 0.13.5-RC1)

This PR will take us onto the Play 2.3 platform :)

It does **not** include Inspect functionality due to a runtime classpath clash that we have decided to wait resolving until Echo supports Play 2.3 and Akka 2.3. Apart from that all functionality should be available.

Although there is plenty of opportunities to refactor/improve the code now that we have Play 2.3 this PR is focused on just getting things working. Any improvements will come in following PRs.

As always feedback is welcome.