Refactored 'Mainmenu' and 'Button' Class

These were written early on in the program and have needed a refactor
for a while...

Whats new:
- Buttons can now be purely text.
- Or purely Texture.
- And still be Texture with text.

Whats broke:
- Mainmenu has to be rewritten... Currently has start button but none of
the others.
- Working on getting mainmenu back to normal now.
- Also PauseMenu needs to be rewritten...

Whats old:
- Original Button Class, MainMenu and PauseMenu are stored in the files
but excluded from the project itself.
- See: Button_Old, MainMenu_Old, PauseMenu_Old