Added support for setting the http status code and response for the maintenance page

Im using aws elb load balancer to host my pages, and if I put the page in maintenance mode the http status code is 503.  This will register in the load balancer as if the node is not working correctly and all my nodes
will be removed from the load balancer and no one would see the page. 

I added two optional new configuration options, and a response listener to change the http status and code
in cases like mine.