Don't have to set subclass_name, UR does it for us
Make software_revision immutable
Make update_status just status

UR has magic to create a __status that is the real accessor.
Make properties of StatusEvent immutable
Restrict permissions for 'gms-user'

They shouldn't be able to delete process.process entries, nor delete or
modify existing process.status_event entries
Deploy with Sqitch and add tag
Merge pull request #200 from davidlmorton/process_improvements

Some small Genome::Process improvements