Fix "This is a development server. Do not use it in a production deployment." warning

[fapdash]

Currently the app starts with this warning:

WARNING: This is a development server. Do not use it in a production deployment.

In the flask documentation it reads:

While lightweight and easy to use, Flask’s built-in server is not suitable for production as it doesn’t scale well.

I don't know if performance is an issue right now but this probably should be fixed down the line. The documentation for using a WSGI server with connexion is here.
Of course the current live deployment would have to be adjusted after this change.

[jnerlich]

Right now we do not have performance issues, but I agree with you that this should be done.