Upgrade to Play 2.2

* [resolves #65129050] database connections shouldn't close randomly
* lessc up to 1.4.2 (from 1.3.3)
* sbt up to 0.13.0 (from 0.12.3)
* akka up to 2.2.0 (from 2.1)

We have a few deprecation warnings in tests and during compilation, but
nothing that should cause any problems for now.

Play 2.2's ActionBuilder is great.