commented out some code that uses GameContainer
removed uses of Slick2d's TextFields
deleted uses of GameContainer in init() od Gameplay
commented out uses of container in init() of Menu
removed GameContainer from init() of GameComponent and subclasses
removed more uses of GameContainer

while keeping the same level of "playability" as before (not really
playable)
removed even more uses of GameContainer
removed unused Slick2d music code
removed alot of Slick2d's Graphics and GameContainer

currently everything is broken