Added Mass and collision to EnemyBase
Added Mass and collision to EnemyBase

Added a Mass and CollisionDamage to the enemy base. Also updated
handleCollision method for EnemyBase to handle the PlayerShip collision.
The Mass of the EnemyBase is super large so that when the player
collides with it, the player effectively just bounces off again at full
speed.

jackinloadup/lunatic-fringe,jackinloadup/lunatic-fringe