Add collision behavior for enemies and player

[cowsintuxedos]

Little happens when the enemies collide with the player. Collisions are already detected and handled by the code - the aggressive goblin causes the player to lose all health when touched. Should extend and add more behavior on collisions.

100 pts?

[steve-fields]

F17 OK (100pts)

[steve-fields]

W18 OK (100 pts)