EMFolderTree: Show connection status icons.

Each network service row in the folder tree now shows an icon which
follows the state of the service's connection status and remote host
reachability.
EMFolderTree: Remove "ellipsize" property.

Always ellipsize folder names, otherwise it interferes with the status
icons.  The property was once bound to a hidden GSettings key, but the
setting was silly and was removed some time ago.