Add "action" drop down menu to term listing

[jzohrab]

Currently the term listing only has "bulk set parent", but there are a few other things that will make sense: bulk delete, bulk set status, add to anki, etc. The cleanest way to do this will be with some kind of Action drop down menu, like this: https://www.w3schools.com/howto/howto_css_dropdown.asp

The "set parent" entry could be disabled as it is currently.

Acceptance tests will have to change.