Implement common query interface

[lutzmor]

Currently the Query type passed to store.findMany is undefined. It needs to be a common interface that makes sense in any store, not just the database store.

• It needs to be mappable to typeorm's FindOptions
• It must be transportable over json
• Considerations for security must be taken (probably avoiding all join capabilities to avoid entity permission leak)
• Consider severely limiting to force controllers to do the querying if security concerns are too great

Another comment by zakhenry

• Consider graphql, it makes sense across multiple database scheme & transports. Tough part may be data hydration