Make less API requests

[rossjrw]

(From #232)

I should also find ways to move away from frequent full-database propagation and towards making on-demand requests to Crom directly, e.g. for .lc. This should not add a noticeable delay and will save us both a lot of bandwidth.

If I lose my attachment to tracking ratings, I should be able to propagate just the titles of existing works much less frequently while sacrificing very little accuracy. I'd still be able to perform regex search and title golf.