Add a UI button for "Copy Paste Includes Sequence Markers"

I love that the “Copy Paste Includes Sequence Markers” can be given a keyboard shortcut, but as it is a toggle, there’s no way to know its current state without clicking on the Markers menu. If there was a UI button (similar to the proxies button) that could be added to the program monitor panel, then it would be much easier to see whether it was active or not. Any other persistent visual indicator would suffice as well.