Porting to Scala 2.11

Here’s a little treat: porting to Scala 2.11 (work in progress). So far dependency and compatibility issues are fixed (see inline comments). However [this change](https://github.com/playframework/playframework/commit/0a3a1fb8bde7f74fcf7c9c1f938de1a30dd1d0c1) in `play-functional` seems to prevent it from compiling correctly. I’ll investigate further.