Use Pango from GI instead of the static bindings
Fix text in the pages icon view

The width of the icons/text was getting huge by default after, so
instead of using the Gtk.IconView's default text renderer, now a
custom one is used, with a maximum width and ellipsize set.

gb#708365
Fix reordering of pages in the icon view

This fix involves removing drag and drop. DND should be added back
without interfering with the reordering of pages in the future.

gb#708109