Many changes

Moved all include files to Main.cpp

Moved STATE variable and gRenderer to a new header Util.h. Varibale
there will work as global variables

Removed a couple of cpp files and moves the implementations to their
respective .h file.

New Classes: Menu, Button

Now we can create Menu objects and insert Buttons to it with images that
we want and we tell each button what state we want it to affect. Render
the menu will render all buttons. Menu class keeps track of which button
is selected. Change selected button with up and down arrows. Press
selected button using space.

Created two new button textures. One for a selected button, one for
deselected.