TilemapVisual; clean up QuadGeometry assumptions, close #168 move to TilemapVisual subclasses where custom geometry can be used. Added geometry_for_tile and geometry_for_layer as convenience. The fixed flag for layers will have an effect on this potentially, but this closes #152
Tilemap; layer; adding fixed flag in preparation for static layers (see #146)
Tests; tiles; change to a random tile ID on iso and ortho map when clicking to test visual connection to map tiles and subclassed geometry types