Content api Client

I have been unhappy with performance since switching from Dispatch to WS based content api client. An easy way to prove/ disprove this is to switch back. The reason for moving off of Dispatch was that it never had a Future implementation, it has one now.

Also cleaned up a bit...

You now mixin a trait ExectuionContexts instead of import play.api.libs.concurrent.Execution.Implicits._