Add more JsonParser tests

[qdot]

• Need a test for schema mismatched system messages
• Need to check for null on return on ButtplugMessageToJObject and Serialize
• Need to either do schema validation or check for null array, not both (redundant)

[qdot]

Could probably use more tests here even though we're client only now. Also yanked the schema to reduce dependencies, so it's important that the parser works.