FilterView should allow filtering on rating

Can't filter on rating (safe, questionable, etc) using `filterView`.

Rating doesn't apply to the tags, but can be applied to the images. [The count of images for the tag wouldn't necessarily match the count of images shown.]

Start by locating the filterView implementation and tracing how filters are applied to images and tags. Check how ratings such as safe and questionable are represented in the SQLite data, then verify that filtering images by rating works without assuming tag counts match image counts.

Written by the indexing model from the issue text.