[FA]{issue} I62 - new enemy type

Closes #62
-Created new enemy type (new body sprite)
-Refactoring of EnemyManager (removal of speed/sprite)
-Changes to tests based on that
-added setting for rotationSpeed in constructor of Entity, Player and
Enemy
-further restructuring of Assets WIP
Merge remote-tracking branch 'origin/fadler_dev' into vadler_dev