Fix up Sakai Pragma, Cache-Control, Expires

Seeing duplicate and old cache control headers:

Cache-Control: no-store, no-cache, must-revalidate, max-age=0, post-check=0, pre-check=0
Cache-Control: no-store, no-cache, must-revalidate, max-age=0, post-check=0, pre-check=0
Content-Language: en-US
Content-Type: text/html;charset=UTF-8
Date: Tue, 11 Sep 2018 16:36:30 GMT
Expires: Mon, 11 Sep 2017 16:36:30 GMT
Expires: Mon, 11 Sep 2017 16:36:28 GMT
Last-Modified: Tue, 11 Sep 2018 16:36:30 GMT
Last-Modified: Tue, 11 Sep 2018 16:36:28 GMT
Pragma: no-cache
Pragma: no-cache
Transfer-Encoding: chunked
X-Frame-Options: SAMEORIGIN
X-Sakai-Session: 35aa4821-a15d-4dc1-96f9-1c737968e79a

https://blogs.msdn.microsoft.com/ie/2010/07/14/caching-improvements-in-internet-explorer-9/
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
https://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-26
https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching

The freshness lifetime is calculated based on several headers. If a "Cache-control: max-age=N" header is specified, then the freshness lifetime is equal to N. If this header is not present, which is very often the case, it is checked if an Expires header is present. If an Expires header exists, then its value minus the value of the Date header determines the freshness lifetime. Finally, if neither header is present, look for a Last-Modified header. If this header is present, then the cache's freshness lifetime is equal to the value of the Date header minus the value of the Last-modified header divided by 10.