fix: try to import cube relationwidget with new and old cube format

cubicweb_skos/views/widgets.py

@@ -17,12 +17,22 @@
 from cubicweb import tags
 from cubicweb.predicates import is_instance
 
+relationwidget_imported = False
 try:
-    from cubes.relationwidget import views as rwdg
+    from cubicweb_relationwidget import views as rwdg
+    relationwidget_imported = True
 except ImportError:
     pass
-else:
 
+if not relationwidget_imported:
+    # try to import old_style cube format if it failed with new_format
+    try:
+        from cubes.relationwidget import views as rwdg  # noqa
+        relationwidget_imported = True
+    except ImportError:
+        pass
+
+if relationwidget_imported:
     class SearchForRelatedConceptsView(rwdg.SearchForRelatedEntitiesView):
         """Specializes relation widget to link to concepts which are expected to be constrained by
         an RQL expression on the edited relation definition.