Made gameImpl also calls dispose of the enemies when they are removed.
Made enemies remove themselves when they are outside the screen.
The implementation is the same as the one used to remove projectiles. This should be updated to use a global "do later" timer once it is implemented.
Revert "Made gameImpl also calls dispose of the enemies when they are removed."

This reverts commit 7ae5358bef629138d19c144ff2951da8d7fdd1b3.
Removed left over timers in model package.
Made simple enemy dispose itself when it is removing itself.
Updated tests.
* Made sure all tests uses the timer from the util package.
* Made sure that remove calls are not allowed while looping in the SimpleMockTimer.
Fixed EnemyImplTest.
Have to trigger a timer "tick" for the remove to go trough.
Merge branch 'development' of https://github.com/Jokab/Bullet-Inferno into development

Conflicts:
	Bullet-Inferno-test/src/se/dat255/bulletinferno/util/TimerImplTest.java