3645 dotted lines everywhere on tag edit pages

http://code.google.com/p/otwarchive/issues/detail?id=3645

We had some overly vague CSS that was leading to dotted lines under every link on Wrangling pages:

```
a.tag, .tags a {
  color: #111;
  line-height: 1.5;
  text-decoration: none;
  padding: 0 0.125em;
  border-bottom: 1px dotted;
}
```

That .tags a bit means that any link inside any element with the tags class will have that style. We don't actually want that: there are quite a few places it would be useful to be able to apply the tags class without restyling all links. Like, for instance, the fandoms and metatags listboxes on that page. Or fieldset labeled Tags on the Post New form. Or some tables I was working on.

Most tags links are generated with a helper that adds the class "tag" to the link itself, e.g. `<a href="http://test.archiveofourown.org/tags/all%20the%20trolls" class="tag">all the trolls</a>`. This removes `.tags a` and fixes the places where links to tags didn't have the proper class.