Update 2.3

Update plugin to work with `Play 2.3`.

Updates:
 - `Clojure` to `1.6.0`
 - `Clojurescript` to `0.0-2342`
 - `play.sbt-plugin` to `2.3.0`

The imports in `ClojurescriptPlugin` also needed to be changed because if `play 2.3`.

The reason for the change of the name from `ClojureScriptPlugin` to `ClojurescriptPlugin` was only because of naming conventions in my IDE, it doesn't really have to change.