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

gajim/chat_control_base.py

@@ -177,7 +177,7 @@ def __init__(self, parent_win, widget_name, contact, acct,
         self.xml.overlay.drag_dest_set(
             Gtk.DestDefaults.ALL,
             self._dnd_list,
-            Gdk.DragAction.COPY)
+            Gdk.DragAction.COPY | Gdk.DragAction.MOVE)
         self.xml.overlay.drag_dest_set_target_list(dst_targets)
 
         # Create textviews and connect signals