Display certain tags at higher levels (item view / search results)

[demiankatz]

In some scenarios, certain tags on items would be useful to see at higher levels (e.g. in dimenovels.org, it would be nice to identify poems/sketches in search results and at the issue level, without having to click through).

It might be useful to add a new flag to the tags table which indicates which tags should "show through," and then we could adjust some queries to incorporate relevant associated tags.