Make Multishell Scrollable
You can now Scroll through the Programlist, if the list bigger than your Screen.

@dan200 Changes are now done
I added a patch from @BombBloke which allow the scroll with the mousewhell.
Just trying this out today and noticed a issue with the scroll offset not changing when tabs are closed:

- Open lots of tabs in multishell (I ran
bgabout 10 times). - Scroll to the far right but keep the focus in the first tab.
- Start closing tabs.
I think the best thing to do would be to ensure the offset is valid before each menu redraw, clamping it if required.
@SquidDev Thanks for reporting. The Bug is now fixed.
Thought I'd commented this a couple of weeks ago but apparently I didn't. Sorry.
@Wilma456 The fix works, but I feel it would be nicer closing a tab scrolled the selection to the left again, so that the whole tab list is always full - rather than just having one tab on the far left.