Update to now provide three Openbox themes instead of the original two.

Two of the themes -- OB-flat-gray menu and OB-flat-black menu -- share a flat light-gray window titlebar to go with today's modern flat looks. However, one has a gray menu with dark gray highlights, and the other has a black menu with blue highlights. The black menu doesn't necessarily match the gray window titlebar; however, sometimes I just want a dark menu.

The third theme -- OB-Flat (black menu and titlebar) -- has a flat-black window titlebar, and the menu is also flat-black with blue highlights. I also changed the window controls so that they are flat-blue when hovered over and flat-red when pressed.

Pipe menus are slightly offset away from the main menu on all three themes.