Move to Twirl for template parsing.

Fixed tests that started failing under 2.11.

* added a strategic `initialize` call before checking `.isAbstractClass`, since
  flags weren’t there yet
* made the stub `play.mvc.Result` a proper public class (default visibility in
  Java is package private). The 2.11 compiler correctly failed those tests.
Merge pull request #217 from dragos/move-to-twirl

Initial move to using twirl for template parsing.