[Inkscape-devel] Automatic mention of shortcuts in tooltips

I've just added code to automatically add the shortcut key to tooltips of verbs. If you find any problems with tooltips (it lists something strange, a tooltip doesn't show anymore, the shortcut is listed double, whatever) you know where to look first.

The main change is that the shortcut is now made part of the tooltip as reported by the verb and that we now use a gtk function to derive the shortcut label instead of our own function (the result seems to be the same). I've tried to check for situations where this would lead to double or unwanted listing of the shortcut, but so far it seems fine.