"[EPIC] Report option on everything - reports models

See #890 (closed)

• Report model/migration
• Serializer to handler report submission (including anonymous submissions)
• Report category to triage reports
• Pod setting to enable/disable anonymous submissions on specific categories
• Really simple API endpoint to submit reports
• read:reports and write:reports oauth scopes
• Generate a proper federation ID for the report
• Store the ID of the mod who handled the report

I'm leaving the WIP status for a day or two, in case I forgot anything important ;)