code: function requestFilter() {
    return function(req, res, next) {
      if (!_isJsonRequest(req) && !_isVoidFilterRoute(req)) {
        return _renderAppShell(res);
      }
      next();
    };
  }
docs: Intercepts request to check whether it is an 'application/json' type
  request which gets passed through, otherwise it breaks the request chain
  serving the Single Page Application HTML shell file.
  @return _void_
  @author Tomislav Capan