Add more filters to `/search`

[lfborjas]

e.g. country, region, timezone, etc. To do justice to all the filters and not end up either requiring them all or mashing strings together, we'll need something less perfunctory than postgresql-simple. I've used persistent+esqueleto in the past, but opaleye is also a good candidate, slightly less template-haskelly (for zero TH, there's always Beam.)