Add preliminary mac menu bar support.

This won't actually work right now since I'm using the cross platform
look and feel. When I fix the problems with the system look and feel
this will make sure the menu bar operates properly.
Switch to system look & feel.

These changes fix the problems I had with the mac  look and feel
buttons. They now properly show their correct colors. I also gave the
buttons borders, in preparation for when I will use the border to
indicate the selected chess piece. This change also fixes trailing
whitespace in the files.