Introduce support for authentication and authorization
- New /authenticate endpoint allows authenticating and acquiring
  authorization tokens.
- If authentication is enabled, and user is not authorized, dissallow access
  to all endpoints other than '/', '/authenticate', '/webadmin' and '/browser'
- API exposes ability to regenerate and set authorization token
- API exposes ability to change password
- On initial startup, user is required to change the default password
- Authorization data is stored in data/dbms/authorization, by default. This
  file can be copied to other neo4j deployments to share authorization config.
Add authentication services to Browser.
Add password popup on password change required.
Moved browser auth to frames, implemented bulk of auth flow. Lots of polish left.