Refactor config file verification to use schema based verification

[mountaindude]

Butler SOS already uses this model, works well.
By making this change it is possible to use the powerful (and actively maintained) tools for JSON verification, for example ajv.

The schema can be verified using this concept, but some Butler-specific values in the config file still need to be verified.
For example verification that custom properties mentioned in the config file really exists in QS.