private void recordReferrer(String region) {
		if (StringUtils.isNotEmpty(region)) {
			CoreLogger.LOGGER.info("Accessed to {}", region);
		}
	}
Return nGrinder index page.

@param user      user
@param exception exception if it's redirected from exception handler
@param region    region. where this access comes from. it's optional
@param model     model
@param response  response
@param request   request
@return "index" if already logged in. Otherwise "login".
ngrinder-controller/src/main/java/org/ngrinder/home/controller/HomeController.java