Completed the TmxData definition and simple tests

 - Real tmx files are loaded in the Tmx unit tests.
 - Although, only simple checks are done to make sure they are valid.
Abstracted the use of RepeatFillRenderer

 - a StaticRepeatFillRenderer takes place of the old one
 - TileMapRenderer is a RepeatFillRenderer with key methods overridden
 - Also a basic design for rendering the individual tiles of the TileMap