Relax json schema validation

[MihaZupan]

This removes a couple false positive errors from the schema config validation:

• It's fine to define bools in json as strings "true"/"false" instead of just true/false
• TimeSpans can parse without leading zeros - 00:2:3 is an acceptable alternative to 00:02:03
• Metadata values can be non-strings in json. E.g. "foo": 42 is okay instead of "foo": "42"