added a config file instead of having to modify the main file

[rlunaro]

This change modifies the index.html file to request a config.json file: with this improvement, the configuration of the application can be made in the config.json file instead of having to modify the main file

[sstidl]

Thanks for the proposed enhancement.
To merge this it has to be backwards compatible. So please modify your changes so it works out of the box with the created docker image.