User relations and message relations

New features, immediate changes, etc.

Solving the current application error.

Technical Description

Using two modes, while we are still using Heroku, which are stored in the APP_ENV variable:

• APP_ENV=docker for when app is running from docker-compose as a service
• APP_ENV=heroku for when app is running from heroku There can be more modes added in the future.

Because this is a critical bug fix, this does not need democratic approval, before being deployed. This is the case, when the app crashed or a security vulnerability has to be mitigated.