Refactors the code that handles monitoring an agent websocket with pings and updating the connection times in the DB.
Consolidates v1 and v2 agent APIs under the same code for this.
One substantive change (not _just_ a refactor) is that I've made it so that we actually disconnect if the agent fails to respond to our pings, rather than the old behavior where we would update the database, but not actually tear down the websocket.
