Enable list suggestions phase 1 (OAuth only)

[tezoatlipoca]

Enable people who are NOT named contributors, listowners or su to add items to a list. Suggested items may either:

• immediate add to list: Items added get a special status "pending" - they show up in the list but they're highlighted in a special way when the list renders (background yellow, special hazard border, dunno)
• "pending" and do NOT appear in the list until approved This setting is "suggestions: off|default-approve|default-pending"

Suggested items are put into a moderation queue for the attention of relevant LO or SU. There needs to be some way to provide feedback to suggestors that their items has been approved or rejected. Appeals on rejection can be made to the su/lo who made the decision or the list creator directly (so we need to check that there is a relevent contact endpoint for that user - email? masto account?) Since we don't have any email facility yet, we must insist on suggestions coming from an OAuth user (again, if they're not a registered local user. Oo good point - if the user isn't a LO or CO on a list but they ARE a valid local user and they can SEE the list and it has suggestions enabled, they are considered a valid suggester just like an OAuth user is. i.e. "anonymous" role on that list.

[tezoatlipoca]

DONE. Use the "mod queue" idea as "reported items", special Moderation list called "MODERATION. From there SU can view item and mark it "visible" in its list.