Option to expand window buttons to fill available space
Similar to how the separator has a means to expand to fill the available space, it would be preferable to have window buttons have this expand option, so that an extra separator isn't needed and it would be easy to right-click the empty space and get easy access to the window buttons context menu rather than jumping through hoops to get to the window buttons dialog, especially when 'show handle' is disabled. This would also resolve #20 (closed).