ChatControlBase: Add support for KDE notification drag and drop

This adds Gdk.DragAction.MOVE to the drag_dest, enabling Gajim to process
dropped items from KDE notifications (for example). Fixes #9011
3 jobs for master in 3 minutes and 57 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #17907
run-appdata

00:00:05

passed #17906
run-tests

00:03:38

 
  Build
passed #17908
run-build

00:00:12