sysprof: Add missing HIG shortcuts

(Draft?)

While playing with sysprof I noticed I couldn't use my ctrl+q muscle memory to quit, or open a file with ctrl+o. I thought of scratching my own itch and adding those and a few more here. Notably this is missing some other HIG suggestions like the shortcuts window, but that seems overkill for such a short menu (?).

Also, this is very clumsy because I wanted to get it to work and ask if it's something you'd like to merge. I think there's a few easy alternatives to avoid some of the current duplication (maybe move some actions to app.? reuse a menu .ui file?)

In any case, happy to iterate if you want to merge something like this 🙂

PS: Yes, I stole the primary_menu boilerplate from gnome-text-editor 😆 😆