Changes to fix memory leaks.
Changes to fix memory leaks.

- Convert the GLKView from an anonymous inner class to a static nested
  class to prevent it from keeping a reference to the enclosing class that
  prevents RoboViewController from being GC'ed.

- Instead of having RoboViewController implement GLKViewControllerDelegate
  and call setDelegate(this), move the delegate to a static nested class.
  This avoids a circular reference that prevents RoboViewController from
  being GC'ed.

Both of these are slight variations of the problems described here:
https://github.com/robovm/robovm/issues/749

This fixes #73.

playn/playn,playn/playn,playn/playn