Pre-moderation tools

[excieve]

Add pre-moderation tools to the admin. This requires a permission group for claim moderators with access to claims only. Moderator group members should only be able to see claims, which have complete status. The only available action should be a change of status so that a claim may be approved or invalidated (with a trace record).

Think about making a custom admin page for moderation that shows maximum amount of relevant info in the list, has two buttons ("approve", "invalidate") and automatically updates the list changes without refresh. This will be easier to do from scratch than customise Django admin.

Think about notifications: browser notifications, emails, browser Push API when moderator is not viewing the page.