NewFeature: pull JSON models from BasicGroup & WebSocketGroup

Using control byte 42 BasicGroup & WebSocketGroup will send to client a JSON serialized model.

```java
    private final byte getJSONModel = 42;
    
    @Override
    public void receive(byte[] data, Connection from) {
        try {
            if (data == null) {
                Log.error("Null rec");
            } else {
                switch (data[0]) {
                    // ...
                    case getJSONModel:
                        ByteArrayOutputStream baos = new ByteArrayOutputStream();
                        JSONModelSerializer serializer = new JSONModelSerializer();
                        serializer.serialize(getModelService().getLastModel(), baos);
                        from.send(baos.toByteArray(), Delivery.RELIABLE);
                        break;
                    // ...
                }
            }
        } catch (Exception e) {
            Log.error("Something bad ...", e);
        }

    }
```