Glance DB refactoring

Before we support more backend db. It's necessary to refactor to avoid replicating current faults to another potential new backends. Below is some items we can improve based on the discussion markwash and me.
1. Remove Context to avoid stamp coupling.
2. Do not expect the db api to do business logic (like who can see what images)
3. Using filter = {…} which is hard to use, makes monster functions, and doesn't cover all the cases we need, it should be replaced
4. The interface is just silly, probably shouldn't be a module full of functions, rather something more OO, similar to the Repo and Models