add refdata endpoints

Created basic  viewsets for refdata models.  
You can try one of the endpoints like this: http://192.168.33.10/api/jobgroup/
Added one extra test for objstore api for coverage

We **could** merge this now, if you like.  It's very simple, and no direct tests.  But I'm not sure if we want **all** of these endpoints.  Let's discuss which ones we may not want.