Fix shortcut display for multi-key shortcuts

Shortcuts like "Ctrl+A, Alt+B" looked broken in Command Bar display. They are now properly displayed. It still isn't super good, you get a display like:

Ctrl + A + Alt + B

Better would be:

Ctrl + A, Alt + B

But maybe that's just my opinion. In any case, this change lays the foundation for further improvements.

Also, if this is okay, we can port it back to 21.04.

Signed-off-by: Waqar Ahmed waqar.17a@gmail.com