schema validation of 'ignored' can fail

[Wilko Henecka]

We have two ways of defining a feature to be ignored in the schema.

1. we just add "ignored": true to the top level of the feature def.
   e.g.:

{
      "identifier": "firstName",
      "format": { ... },
      "hashing": { ... },
      "ignored": true
},

2. as a shortcut, we can also just have "identifier" and "ignored"
   e.g.:

 {
      "identifier": "id",
      "ignored": true
},

The way the schema def is written, the validator cannot disambiguate between the definition for 1) and 2) if you provide the example for 1).
You get an error saying: ... is valid under each of {'$ref': '#/definitions/ignoreFeature'}, {'$ref': '#/definitions/featureConfig'}