Removed warnings
More Gui changes

FEATURES:
- Finished GuiControlButton
- Updated to OpenGL ES 2.0.  This allows for shaders.  This was done to
help with font rendering, along with the fact that GLES 2.0 is being
removed from LibGDX
- Instead of using `Gui`, we now use LibGDX’s `Screen`.  This allows
for better integration with GDX.
- Redid the distance field system to use shaders - this allows for
clearer rendering and anti-aliasing
- Remade the Arial font (it was prepared incorrectly before).