Adding main menu to the GUI

[yugeshk]

There are two three options for the menu bar that the UI can have. I have written two mocks that can be found under the gui-devel branch at the moment (while i organize the master with other branches). The third (which is usually the recommended way to go is currently blocked because of deprecation of Gtk.UIManager etc) but I will try to port it to the newer framework and put it up under mocks too.