Create Boku Seller Resource in Solitude (bug 989502)

- Create BokuSeller Model
- Create BokuSeller Serializer
- Create API endpoints to interact with BokuSeller
- Add tests for serializer and views
- Update boku-basic.py test script to talk to API correctly
Merge pull request #207 from JaredKerim-Mozilla/989502

Create Boku Seller Resource in Solitude (bug 989502)