Delete tagged graphs

Now you can delete graphs by tag from tag_graph view!
The later case looks no problem because the query when running `#delete_all` is as follow. 

```
DELETE FROM `nodes` WHERE `nodes`.`id` IN (SELECT id FROM (SELECT `nodes`.`id` FROM `nodes` JOIN taggings nodes_taggings_29f4e31  ON nodes_taggings_29f4e31.taggable_id = nodes.id AND nodes_taggings_29f4e31.taggable_type = 'Node' AND nodes_taggings_29f4e31.tag_id = 39 WHERE `nodes`.`type` IN ('Graph')) __active_record_temp)
```