No support for unicode characters if json content-type

``` python
        elif content_type == 'application/json':
            try:
                request_json = json.loads(request.body.decode())
                assert isinstance(request_json, dict)
                return request_json
            except:
                raise HttpError(HttpResponseBadRequest('POST body sent invalid JSON.'))
```

i believe this code should be refactored
