Added EventDispatcher support to SpriteSheetBuilder and BitmapAnimation. Added SpriteSheetBuilder.onComplete & .onProgress.

Signed-off-by: Grant Skinner <info@gskinner.com>
Fix to BitmapAnimation's event dispatching.

Signed-off-by: Grant Skinner <info@gskinner.com>
EventDispatcher fix.

Signed-off-by: Grant Skinner <info@gskinner.com>