code: function parseResponseType (req) {
    if (req.query && req.query.responseType) {
      if (req.query.responseType == 'modal') {
        // suport for old we.js contentOnly api
        req.query.responseType = req.we.config.defaultResponseType;
        req.query.contentOnly = true;
      }
  
      req.headers.accept = mime.getType(req.query.responseType.toLowerCase());
    }
  
    if (req.accepts(req.we.config.responseTypes))
      return;
  
    req.headers.accept = req.we.config.defaultResponseType;
  }
docs: Parse the response type
  
  with order: 1. extension, 2.responseType, 3.Accept header
  
  @param  {Object} req express.js request
  @return {String}     the response type string