HFP-4063 Add support for user configuration file

[otacke]

When merged in, will add basic support for a user configuration file (not sanitized or further). As proof-of-concept it allows to set the user state save frequency.

[rezeau]

That would be quite useful.

[devland]

@otacke I hope you don't mind that I took the liberty to extend your idea so that the user config feature can also overwrite the values from the config.js file. :)

[otacke]

@devland Not at all :-)