Remove all references to `Shot`s

* References to the shots were still being maintained in the
* `_playerShots` and `_enemyShots` Lists, not allowing the `Shot`s to be
* garbage collected.
	* That's why the game got really slow when left on -- shots would
	* accrue from enemies, leading to the `_shots` array to grow
	* superhuge.
Remove extra references to shots and enemies
Clean up Shots

* Changed ShotContainer to ShotManager
* Lots of cleanup
* Made sure that ALL references are deleted to both `Shot`s and `Enemy`s
Merge
Merge pull request #7 from registered99/shots_cleanup

Remove all references to `Shot`s