SeqAuto model changes

Historical note: SeqAuto was written to run on a private intranet in a lab - where everyone could see everyone else's data etc (unlike VariantGrid.com where multiple labs share the system and don't want to see everyone's stuff). It also used to do the whole scanning on drives etc run by the system, so we assigned things to `settings.SEQAUTO_USER`. Now, we have an API, where users connect and send things up.

Do this after API work, so it's easier to cherry-pick commits back to SAP branch

But before VG4 upgrade

* Add a user, and guardian permissions to all objects
* EnrichmentKit should have unique_together name/version
* SequencingSample unique_together sample_sheet/ sequencing_sample_id
* There was some model that was regarded as a SeqAutoFile or whatever and wasn't actually a file - double check