Collision detection

[rijkvp]

• [x] Create a function in the grid class that transforms screen coords in to grid nodes. The opposite of what is done when drawing the nodes.
• [x] Create a function that gets the adjacent grid nodes of the player
• [x] Create a separate tab in processing that contains the collision detection functionality
• [x] Stop the movement of the player when colliding with a wall
• [x] Prevent the player from moving into walls

[rijkvp]

It works!