Allow grid columns to be *invisible* (but still present in grid)

this can be useful when you need contextual data for a given row, for
sake of front-end UI features, but do not want to actually show the
extra data column(s)

tailbone/templates/grids/buefy.mako

@@ -176,7 +176,10 @@
 
       <template slot-scope="props">
         % for column in grid_columns:
-            <b-table-column field="${column['field']}" label="${column['label']}" ${'sortable' if column['sortable'] else ''}>
+            <b-table-column field="${column['field']}"
+                            label="${column['label']}"
+                            :sortable="${json.dumps(column['sortable'])}"
+                            :visible="${json.dumps(column['visible'])}">
               % if grid.is_linked(column['field']):
                   <a :href="props.row._action_url_view" v-html="props.row.${column['field']}"></a>
               % else: