Delete tagged graphs

Now you can delete graphs by tag from tag_graph view!
drop down version
http://gyazo.com/3788f5a90674bb73d1581268a5ceeccc

button version
http://gyazo.com/4d60efb030309f479f1cbb68b6ebc936

@sonots Which version do you like? In my opinion, button version is too conspicuous. I like drop down version.