Some fixes to the error handling based on preliminary testing, added missing fields to post, put and get, swagger, added missing serializer fields, new exceptions.
Code should be tested in case of serious/stupid errors.
Merge branch 'devel' of https://github.com/koulutuksenpilvivayla/pilvivayla-basaari into devel

Conflicts:
	sites/basaar/settings.py
Merge
Merge branch 'devel' of https://github.com/koulutuksenpilvivayla/pilvivayla-basaari into devel

Conflicts:
	sites/basaar/settings.py