Update some database fields to use field names consistent with the models

This requires a database migration for existing collections / documents in
the database.
Create PublicGroup and UnlistedGroup models
Grant access to Public group to all users, including those not logged in

Remove support for the demo user.
Don't show a Login button on home page if already logged in
Merge branch 'public-unlisted'

* public-unlisted:
  Don't show a Login button on home page if already logged in
  Grant access to Public group to all users, including those not logged in
  Create PublicGroup and UnlistedGroup models
  Update some database fields to use field names consistent with the models