ui: remove the application menu
https://wiki.gnome.org/Initiatives/GnomeGoals/AppMenuRetirement
We need to stop using the AppMenu. That mean we need to rethink the menus layout.
- Add a main menu in the HeaderBar (doesn't exist yet)
- Remove the other "hamburger" menus and turn them to "kebap" menus.
- Think of the menu bar.
Edited by Hubert Figuière