Add caching headers to the responses for the Rails SAML controllers

According to the [SAML 2.0 Bindings](http://docs.oasis-open.org/security/saml/v2.0/saml-bindings-2.0-os.pdf) the cache headers (`Cache-Control` and `Pragma`) on the HTTP responses must at least contain the `no-cache, no-store`.

* Adds the cache headers on the HTTP responses for the Rails SAML controllers
* Changes the `extend` hook for the `include` hook on the `Rails::ControllerHelper`