Add XP and Vista feature of combining buttons when taskbar is full

[vindasal]

RetroBar is in a pretty good place functionality-wise now, but it's missing one crucial element from XP/Vista that can be very useful to have. By default in XP/Vista, the taskbar buttons of a single program will combine when the taskbar is full, saving space. This feature still existed in the Windows 7-10 taskbar but is slightly different, it does not show the number of windows on the button anymore.
It would be great to have this option, especially for small laptops that have rather low-res screens the taskbar becomes crowded quickly. Even on 1920 width I fill the taskbar constantly. Obviously, this should be optional, but given that this is standard behavior in XP/Vista it should be included if possible.

[pedroeloy]

For me this is the most important feature that is missing from retrobar.