query past scan results

[sydneyli]

Currently, we dump all the scans as blobs into a table, and right now we only support querying the most recent scan for a domain.

let's make it possible to be able to look up all the failures in a given time period for a particular domain or set of hostnames. This is a tracking issue for this functionality, because it's a big change.

• [ ] #132 Migrate to an "ORM"
• [ ] #140 DB schema clarification and migration