Convert /products/<id> to serializer.

Convert /products/<id> to serializer. Not done -- field names?
Add ext to prod/prep tests based on api model
Merge pull request #13 from osu-cass/enhancement/17331

Convert products/<id> to serializer
Use serializer for /vendors/, update tests for new time format/phone
Change No Vendors to information (from error)
Update second No Vendors test to information
Merge pull request #15 from osu-cass/enhancement/17319

Merge vendor serializer into develop
Update /products/vendors/<id> to use serializer
Change vendor product list to serializer, update docs with new times
Change empty list to information from error
Merge branch 'enhancement/17325' of github.com:osu-cass/whats-fresh-api into enhancement/17325

Conflicts:
	whats_fresh/whats_fresh_api/views/vendor.py