Add (back) missing sort button for specialowner cases.
Thanks to Karen for figuring out the bug (my bug).
Fix loadDirList which used two names for the callback function,
cb and callback, so one path failed.
Add functions for creating and clearing the model for a pane.
Clear modelForPane.activityDir when file is changed (not sure if
I got all the places this should be done).
Changed isActivityDir to checkIfActivityDir, so name doesn't imply
that it returns boolean; also changed detection so that it matches
the behavior of loadTemplateMetadata.