Use masks for sprites

[JoshuaU01]

Use masks for collision handling etc. between sprites instead of rectangles.

[JoshuaU01]

1. masks for all objects/sprites
2. mask based collision detection (2.1. additional rect based collision detection for performance reasons)
3. calculate mask overlap with collide_mask() to ensure correct behavior in position update methods
4. draw masks manually for all character and object models (must not be too precisely)
5. mask based jump attack of the runner
6. character lights up for a short time when hit