Migrate gallery.go and validations.go to goqu

This one might be the most challenging part of the goqu rework.

-  `GetGalleries` function is very elaborate and prone to bugs if not converted carefully.
- `UpdateGallery` can probably be refactored to be much shorter and better written overall. The Jet library made it hard to do partial updates.
- `NeedsUpdate` isn't used anywhere currently and can be pretty much ignored
