Upgrade to Scala 2.11

Includes:

 * LiftJson -> Json4s, as the latter isn't tied to the glacial Lift release cycle
 * Play 2.2 -> 2.3, unfortunately involves having to import the Application everywhere WS is used.
 * Replacing the old playMagenta plugin with riffraff-artifact. 
 * Moving the docs to where they're on the classpath without monkeying around.
 * Upgrading scopt, which has pretty much completely changed the syntax
The latest versions of sbt-assembly has sensible defaults for all this stuff, so we no longer need to configure it manually.