Add mnemonics to entries in window context menus

Apologies if this is the wrong repo - please file into the correct one, and let me know if there's a guide to new users for identifying the correct repo to file issues in (something like ubuntubug -w would also be useful).

The issue I want to report is that I've developed muscle memory for moving windows around multiple screens when the mouse isn't working/visible by pressing Alt+Space, followed by v (or m). In GNOME, it seems there are no accelerators for Minimize/Maximize/Move or the other commands: