Stop raising an error if view doesn't define row grid columns

just show whatever is gonna show by default; they can edit list if they want

tailbone/views/master.py

@@ -461,8 +461,6 @@ class MasterView(View):
     def get_row_grid_columns(self):
         if hasattr(self, 'row_grid_columns'):
             return self.row_grid_columns
-        # TODO
-        raise NotImplementedError
 
     def make_row_grid_kwargs(self, **kwargs):
         """