Add Support for Play 2.3

Play changed the WS API a bit in 2.3 so upgrading to 2.3 took a little bit of work. Here it is tested against 2.3.0-RC1. Note I changed the version number from `3.0.0` to `4.0.0-SNAPSHOT` since this is a non-backwards compatible change. Not sure if that's how you guys want it.