FEATURE: Supply minimum, required configuration via environment variables for docker setup

[stefanreimers]

I would like to suggest that all necessary parameters for the setup of alf.io can be supplied via environment parameters, including

• Base Application URL
• E-Mail Provider
• Map Settings
• Admin username
• Admin Password

This would allow an unattended, giving the advantage of

• an application admin does not have to ask the infrastructure admin about the password in the docker logs
• an application admin does not have to supply the information on first sign in