Remove all Heartbeat v1 stuff

This removes all the Heartbeat v1 stuff and adds a HeartbeatV2API view
shim. Leaving the shim just makes some things a little easier so I don't
have to undo and then redo all the urls.py stuff.
Merge pull request #378 from willkg/ditch-heartbeat-v1

Remove all Heartbeat v1 stuff
[bug 1092296] Implement heartbeat v2 data model