[bug 1092299] Implement Heartbeat v2 API

* implements the v2 API relying more on the DRF serializer validation
* implements new tests
* fixes issues with the model by nixing the db table and recreating it
* adds a survey admin
Merge pull request #384 from willkg/1092299-heartbeat-v2-api

[bug 1092299] Implement Heartbeat v2 API