ui-utils: port the password storage helper to GtkPopover

GtkMenu and friends are all gone from Gtk4.
6 jobs for lr/gtk-4.0 in 13 minutes and 44 seconds (queued for 3 seconds)
latest
Status Name Job ID Coverage
  Build
passed fedora28_dist #1584318

00:04:13

 
  Test
passed centos7 #1584323

00:09:29

passed fedora_autotools_full #1584322

00:03:10

passed fedora_autotools_minimal #1584321

00:02:27

passed fedora_meson_full #1584320

00:05:11

passed fedora_meson_minimal #1584319

00:05:02