Advanced field definitions

[jneug]

Allow fields to have more complex logic. String values are normal default values, while a dict defines an advanced field. The dict should at least have a type key to determine the field type and usually a value key.

The default value could than also be defined as an advanced field with

{
    "fields": {
        "FieldName": {
            "type": "default-value",
            "value": "my default"
        }
    }
}

This would allow for more complex types of inputs. e.g a file select type.