circles crud

requires relations between Circle and Person domains.

TODO:
- [ ] `Circle.find`
- [ ] test `GET /circles`
- [ ] `Circle.get`
- [ ] test `GET /circles/:id`
- [ ] `Circle.create`
- [ ] test `POST /circles`
- [ ] `Circle.update`
- [ ] test `PUT /circles/:id`
- [ ] `Circle.remove`
- [ ] test `DELETE /circles/:id`
- [ ] `Circle.get(id).get('members').find`
- [ ] test `GET /circles/:circleId/members`
- [ ] `Circle.get(id).get('members').get`
- [ ] test `GET /circles/:circleId/members/:memberId`
- [ ] `Circle.get(id).get('members').create`
- [ ] test `POST /circles/:circleId/members`
- [ ] `Circle.get(id).get('members').update`
- [ ] test `PUT /circles/:circleId/members/:memberId`
- [ ] `Circle.get(id).get('members').remove`
- [ ] test `DELETE /circles/:circleId/members/:memberId`