This would be pretty easy to add, the only difficulty
is that there are no translatable strings that can be
used here. The ones in the other menus have mnemonics
which don't work in a tooltip. I could make a patch to
add tooltips, but I wouldn't know how to get around
this translatable issue except require duplicate
strings in the pot files without underscores/mnemonics.
Also, I think the order of the arrows on the toolbar
should be changed. It currently is < > |< >|, I think
it would be more practical for it to be |< < > >|. This
is just my opinion. Great program, btw.