Pools as a top level window

Pools have now been added to the db. To take advantage of this, a pools window might be appropriate.
- Show pool names
- Ability to filter on pool names
- Selecting a pool sets the image list to the images in the pool

Start by locating the existing viewer window, image-list handling, and the SQLite pool tables. Check how pool names can be read and how image selection currently updates the list. Done means a top-level pools window shows pool names, filters them, and updates the image list when a pool is selected.

Written by the indexing model from the issue text.