Minor fixes for consistency
Changed default value for LayerDepth property of Sprite to 0.5 - placing bodies at 0.5, clothes at 0.4 or 0.3, backgrounds at 1 (for now); Killed Tycho :(
Removed player property from MyFirstGame
Playing around with tiles
Removed ability to move diagonally (prepping for collision detection - it complicates things); Other minor refactoring
Added ICollisionDetector and CollisionDetector; Added CollisionDetector, Top, Left, Bottom and Right properties to SpriteGroup, added spriteGroups paramter to Update method