Accelerator keys in Qt menus

Spawns from #299 Improve usability for users with disabilities

Menus in Qt don't have accelerator keys. That's because I think adding accelerator characters to menu item labels complicates the localization process (All localizators have to be aware of the position of them item in a menu to wisely choose an accelerator character. This is not doable).

First, I need to make some research. There has to be someone who thought of an elegant solution somewhere.

Second, if I don't find anything, I was thinking of automatically assigning accel keys on menu creation. This should be relatively simple (I remember in Delphi's VCLs there was an option to automatically do it, but I didn't find that option in Qt). Just create a set of all available characters, then go through menu items finding the first letter of the label to still be available in the set and insert a "&" in front of it.