gtk: setup setting inApp menu
gtk: setup setting inApp menu

Per the GNOME Design initiative to remove the usage of the in-app menu and replace it with a primary menu in the application itself. We already have everything moved to the primary menu.
Fixes #1629
gnunn1/terminix,gnunn1/tilix,gnunn1/terminix,gnunn1/tilix,gnunn1/tilix