Add friendly HTTP responses


Add following HTTP Responses:

* JSONResponseForbidden
* JSONResponseBadRequest
* JSONResponseUnauthorized
* JSONResponseNotAcceptable


Add optional "status" param to response.

```python
def JsonResponse(data, dump=True, status=200):
    try:
        data['errors']
    except KeyError:
        data['success'] = True
    except TypeError:
        pass

    return HttpResponse(
        json.dumps(data) if dump else data,
        mimetype='application/json',
        status=status,
    )


def JsonError(error_string, status=400):
    data = {
        'success': False,
        'errors': error_string,
    }
    return JSONResponse(data, status=status)