API change for future compatibility: Non map tile based rendering

It should be possible to support MOS and/or VectorMaps based map rendering.
Therefore the Plugin API has to be redesigned in the following way:

• two levels of abstraction (virtual class levels)
• one for low level frame based custom drawing of everything
• another one that is built on top of the first one, offering a tile-production interface

This would also allow for an easier implementation of the copyright watermark.