TileRendererBase: Add interface TileRendererNotify, to notify implementing GLEventListener about attached/detached TileRenderer

.. since GLEventListener's reshape(..) method must query certain tile renderer attributes (tile pos and image size),
they have to be aware of the TileRendererBase.

To simplify such awareness and hence automate this attachement and passing over the tile renderer reference,
they should implement this new interface.

Gears example implements the new interface,
which caches the TR reference and pauses rotation.