Automate the registering process

[Aloike]

If the application runs for the first time, it doesn't have any credentials. The operator currently has to manually ask for a new app_token through the --register option.

• If no app_token is available, the application must do the call by itself and monitor the request state (see "Track authorization progress" in the login API)
• The application must emit status messages as InfluxDB Line Protocol data points to communicate its status (app_token/registration, auth_token/session, session duration, etc.