Depend on GTK+ 3.11.6

For GtkPopover, including integration with GtkMenuModel

https://bugzilla.gnome.org/show_bug.cgi?id=724480
Use a popover to change modes, not a gear menu

This packs the mode label (presently the header bar title) into a
GtkMenuButton, which uses a popover for changing the mode.

https://bugzilla.gnome.org/show_bug.cgi?id=724480
Close the popover after changing mode

https://bugzilla.gnome.org/show_bug.cgi?id=724480
Focus the input field after changing the mode

Otherwise, you need to click on the input field before you can enter any
numbers. Spotted by Arth.

https://bugzilla.gnome.org/show_bug.cgi?id=724480
tests: update role for radio button when popover is used

https://bugzilla.gnome.org/show_bug.cgi?id=724480