Simpler to spawn an enemy to debug it.

Simply uncomment one of the five debug"Type"(); functions in the
constructor of PrimeEnemySpawnerStrategy to spawn only that type every 5
seconds.

https://github.com/ugly-potato-guy/potato-tap/issues/65
Sprite and code for big alien dying

https://github.com/ugly-potato-guy/potato-tap/issues/47
Hurting sprite for the big alien, and some code

https://github.com/ugly-potato-guy/potato-tap/issues/47