Update to play 2.2.0

Because play 2.2.0 GA is released & play2-couchbase is still in pre-alpha stage. So I think we should use play 2.2.

TODO: I think we should split to several sbt project.
Ex, CouchbaseCachePlugin should be in a separate project (similar to the play-cache plugin in the framework. @see https://github.com/playframework/playframework/blob/master/framework/project/Build.scala)