Support Play 2.2.0

Hi,

This is a small update to make metrics-play compatible with Play 2.2.0 - mainly changing the expected type returned from actions, which in 2.2 is always a `SimpleResult`. Details on the result type change in the [2.2.0 release notes](http://www.playframework.com/documentation/2.2.x/Highlights22).

Howy