Fix orientation events, handlers, and stage orientation in sample.

There were some issues with how Android devices handled the StageOrientationEvent, and runtime
issues how Android handled accessing the stage. This fix corrected both issues. Use addedToStage
and removedFromStage on View to add event listener. Use stage.deviceOrientation to detect the
orientation of the device.
Merge branch '#7/fix-hello-orientation-sample-for-android' into develop