drag and drop in roster
drag and drop jpg/png to roster:
image is not handled in:
roster_window.py:4408 function "def drag_data_received_data()" (info = 0)
Do we need to init drag and drop to get the proper 'info' on file drop? ToDo: look at "chat_control_base.py":270 (Init DND) gtk docu: https://developer.gnome.org/gtk3/stable/gtk3-Selections.html#GtkTargetEntry