Domaind dedicated table

See #580 (closed)

This MR includes:

• A new "Moderation" link in the sidebar administration menu
• A new moderation permission on users (and removes unused federation and upload permissions)
• A new domain table, so we can query domain-related data easily (and prepare for moderation policies applied on domains). This include the migration script to rebind actors to the proper domain instances
• Two new pages: domain list (to list known domains), and domain detail (as shown in the screenshot below), to review domain data such as storage usage, activity, etc.