Collection level Access control

[pgulley]

Implement access control over collections at the user level.

Ie: "Expert A owns Collection B, and only staff_users and Expert A can make edits to the contents of Collection B"

Considerations required for source-level concerns, since they span collections.

[philbudne]

In the past I've wondered if collection editing could be allowed by group: Each collection has a field saying what group it "belongs to", which would be NULL much of the time.