Move get_url_name to base ViewSet

wagtail/wagtailadmin/viewsets/base.py

@@ -11,3 +11,6 @@ class ViewSet(object):
 
     def get_urlpatterns(self):
         return []
+
+    def get_url_name(self, view_name):
+        return self.name + ':' + view_name

wagtail/wagtailadmin/viewsets/model.py

@@ -18,9 +18,6 @@ class ModelViewSet(ViewSet):
     edit_view_class = generic.EditView
     delete_view_class = generic.DeleteView
 
-    def get_url_name(self, view_name):
-        return self.name + ':' + view_name
-
     @property
     def permission_policy(self):
         return ModelPermissionPolicy(self.model)