Unify keyboard shortcuts treatment via priority flag

Submitted by Mr and Mrs D

Assigned to Jérôme Guelfucci

Link to original bug (#10743)

Description

There are two screens i am aware of i can set hotkeys - App Menu > Settings > Keyboard > application shortcuts tab and App Menu > Settings > Window Manager > Keyboard tab. This led me to surprises as Ctrl+Alt+D showed me the desktop instead of Dropbox.

Expected: common namespace for shortcuts - conflicts are resolved with a priority system (exposed in the UI). As of now the Window Manager shortcuts (show desktop) have highest priority but that is not necessary.

The window manager should be the central point of control - the App Menu > Settings > Keyboard > application shortcuts tab should managed by the window manager and applications (including the xfce session) should register their shortcuts there. If they do not their shortcuts should by default have the lowest priority. The system should be extendible with scripts