Create new Worker Presence data structures

[mark-mockett]

(Updated 10/1 to reflect recent revisions)

This PR addresses #182

Summary of changes

• Add a new property worker_presence to the RoadEvent object with data type WorkerPresence object
• Remove RoadEvent property workers_present
• Create new WorkerPresence object with the following properties:
  • are_workers_present – Boolean
  • source – WorkerPresenceSource enumerated type
  • worker_presence_last_confirmed_date – string; datetime
  • confidence – WorkerPresenceConfidence enumerated type
  • definition – array of WorkerPresenceDefinition type
• Add new enumerated type WorkerPresenceSource
• Add new enumerated type WorkerPresenceDefinition
• Add new enumerated type WorkerPresenceConfidence
• Update v4.0 JSON schema
• Update all references to workers_present in the examples to use new worker_presence property

[j-d-b]

I may have missed a meeting on this because the last worker's presence meeting I attended there was not agreement on implementing it this way nor was the discussion in the issue or in person resolved. Not all comments in the issue have been addressed. I would strongly advocate for more discussion before the changes are proposed, as it is much harder to go back and change things than to do it right the first time.

Right now it feels like mostly this just adds a lot of complexity that most members (from the meetings I attended) do not care about.