First stages of converting GameplayScreen into stages.
Merged master
Minor changes
Tweaked ResourceManager to support BitmapFont and refactored a lot of its code.
Upgraded libGDX to March 29 nightly build.
Upgraded to nightly build. Now the screen is black.
Fixed black screen.
Successfully finished migration to new libGDX nightly build

The stage now properly works
Refactored a lot of the code to make it a bit more readable

Still not functional
Updated button images to fill entire image.
Implemented Start button on the top bar

To start a wave now requires to press the Start button.
Renamed World1 to DefaultLevelGenerator
Finished rebuilding GameplayScreen to utilize a Stage