Introduce API v20200611

[corygehr]

• Namespace renaming.
  • CovidSafe.Entities.Reports becomes CovidSafe.Entities.Messages to clarify purpose.
• Object renaming.
  • SelfReport* objects become NarrowcastMessage* to clarify purpose.
• Add API v20200611.
• Renames AreaReportController to AnnounceController.
  • Note this implicitly changes /Messages/AreaReport to /Messages/Announce, which is done for consistency with the PACT paper.
• Tag API v20200505 as deprecated
  • Important: it may still be used via the api-version URL parameter but should no longer be used in new deployments.
• NarrowcastMessage now only allows a single AreaMatch (now NarrowcastArea) per object.
• HEAD /Messages/List and GET /Messages/List now expect int for latitude/longitude to prevent data over-exposure.
  • This is reflected in Region.cs as well.

[corygehr]

@ataymano the Build failures occur in the RegionHelper tests, which is to be expected until your updates have been made. If you don't want to override that failure when approving and merging, feel free to just work from my branch (cogehr/api-version-20200611). I don't plan to do anything else unless necessary.