This 1.16 release improves load time of compare tests across
different projects, creates a default authentication group so
that users have object-level permission and allow download of build
attachments.
Complete list of changes going in:
* frontend:
* add URL for downloading build attachments
* add test history link in test list
* allow serving files from database
* compare: improve compare load times
* fix attachment downloads
* test the actual response contents of all download urls
* add migrations to create auth group and add users
* api: rest: add more status details
* attachment: add a sample unit test
* core: store Attachment's mime-type in the model
* pytest: only check coverage on ci