[FA]{issue} I54 - LightingManager

Closes #54
-Created LightingManager
-Move lighting related code into it
-Changed depending code accordingly
[FA]{refactoring} Box2d bodies for cells

-on creation of LightingManager an ArrayMap (cell, body) gets created
and is filled with the door cells and according bodies
-using a cell now turns the according body on / off
-doesn't have to iterate through all bodies now due to the ArrayMap
[FA]{issue} I49 - Asset Manager

Closes #49
-Implemented usage of AssetManager for texture atlasses (atm: player,
skin) and sounds
-For now the loader blocks each time it loads something.
[FA]{other} I23 - Improve Main Menu

Closes #23
-Created background image and added it to the menues
[FA]{issue} I20 - own texture for enemy

Closes #20
-Created own texture for enemy (watchman)
[FA]{issue} I55 - Disable Flashlight when in body

Closes #55
-Created a method in LightingManager that checks whether a position is
inside a body
-Useing that method in Flashlight to see if the light is inside a body
and disable / enable it based on that