Tweak: changed how the gameFrame is invoked
Bug: removed the location setter from the constructor, because before `pack()` is called the frame doesn't have dimensions.
Tweak: stages no longer directly stop/start the game loop. The game loop is always running, but if a stage State `running` is false, then the stage is not updated.
Tweak: renamed the "keyboard" package to "input"
Tweak: KeyManager now returns previous and current keys as ArrayList<Integer>
Tweak: stage as a new method "preUpdate" that's called before the "update" method
Cleaned up the project. Clean Slate for the game
Added a default Entity class
Tweak: moved the stage package one level up
Added a map Map class
Added unimplemented Snake and Food entities