Fix models states in lastest migration
The timestamp field is used constantly to determine the latest version of a document, index it
Make API writable
Add missing db_index=True option, ref: 5e21b91b24c9972da0956ab599f535466d73a168
Allow documents with no versions to exist, previously these were considered an anomaly and were unhandled
Add support for per HTTP method permissions checking
Update documents app API views to use the new per HTTP method permissions checking
Update tag app API views to use new per HTTP method permission checking