Refactor

[chrisrobidas]

Refactor the following:

• Use GameManager Singleton to keep track of the status of the game
• Use UIManager Singleton to display or hide UI elements
• Use AudioManager to play music and sounds
• Separate UI from logic by making UI listening to Actions
• Separate code that should be separated
• Clean up and rename variables and methods

[chrisrobidas]

Took 3h to complete.