VID-2082 VideoHandlerController::getVideoList cache in memc and varnish

RFCR @garthwebb @macbre 

This method is being called a lot. Let's cache it to reduce the stress it imposes on database and backend servers.

https://wikia-inc.atlassian.net/browse/VID-2082
Why not use an anonymous function here, instead of using ``$videoListGetter``?