Thunar GTK3 deprecations

Deprecations and warnings found in 51fa8fc

Deprecated functions related to the items below will not be handled in this cycle:

• gtk_action_*
  • GAction is not a straightforward replacement
• gtk_image_menu_item_*
  • Gnome decided to remove icons from menu items, Xfce didn't.
  • The official workaround (wrap an image and label in a box) results in an ugly left padding.
• gtk_radio_action_*
• gtk_status_icon_*
  • Gnome decided to drop tray icons, Xfce didn't.
• gdk_threads_*
  • Drawing only on main thread requires lots of refactoring.
• gtk_ui_manager_*
  • GtkBuilder is not a straightforward replacement
• GTK_STOCK_DISCONNECT
• gtk_menu_item_set_right_justified

make clean && make 2> build.log

grep "warning:" build.log | wc -l
0 (out of 1336 when merged)

grep "warning:" build.log | cut -d: -f5 | sort | uniq -c | sort -n -r
# none