Eliminate unneeded permission assignment callback in deposited_by_bill trait.
DRY
Dry up repeated code in the transformations spec with a context setting helper method.
Merge branch 'feature/nu_file_redo' into feature/test_cleanup

Merging in nu_file_redo so I can write tests over it.
Adds more fixture file types to do testing with.
Update title to refer to core files as not generic files, adds a factory with a transient attribute that allows depositor set.
Content creation job now sets permissions.

Also reimplements a refactored content_creation_job_spec.
Moves all of our sample files into spec/fixtures/files/, updates relevant tests.
Content bearing objects created with this factory now have the titles they'd actually have if they were spun up through the front end.