Bug 801909: Port /credits and /credits/faq to bedrock.

* Add credits CSV file processing.
* Add FAQ and Credits templates.
* Add cron command for updating credits.csv from svn.
* Add new app for updating external files.
* Add updating external files to deployment.
* Add apache rule and cache headers.
* Add support for last-modified header based on date from web server.
Basic styles for Credits FAQ page (Bug 801909)
Merge pull request #2131 from pmclanahan/port-credits-801909

Bug 801909: Port /credits and /credits/faq to bedrock.