Added appropriate collision detection responses, block pushing behavior

Altered collision behavior basics. Mouse doesn't die when it hits a rock or block. Cats and yarn hitting barriers also no longer kill the mouse. 

Made a function that returns the x,y coordinates of the desired square based on a direction. Altered the move function to use that function.

Added block pushing behavior that is mostly correct. Blocks will chain when they move, they stop at rocks and edges, they fall into sinkholes. They do not yet move cats or yarn.