[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
[bug 1092300] Add Heartbeat v2 debugging views

* add a view for data letting us verify that packets are coming in
  correctly
* add a view for the error log letting us diagnose and fix errors
Merge pull request #385 from willkg/1092300-hb-v2-views

[bug 1092300] Add Heartbeat v2 debugging views
Rework env view to show python and django version
[bug 1087387] Add feedback_response.browser_platform
Merge pull request #386 from willkg/1087387-add-browser_platform

[bug 1087387] Add feedback_response.browser_platform