[FA]{issue} I48 - Visibility Icon + Refactoring

Closes #48
-Now an icon gets displayed based on whether the player is in a light
-Added getCenter() method to Entity (since the same calculation was used
over and over again)
[FA]{issue} I18 - Player Sprite

Closes #18
-Redid player sprite
-Now with more arms!
-redid animations and .pack accordingly
-Resized stealth icon to 32x32 and repacked the gui images
-Some minor restructuring of the Assets WIP folder