VID-2142 Create a way to clear the VideosModule Video Cache

* Refactored the VideosModule into different subclasses for each video sources
* Added cache purging code
* Incorporated James' AsyncCache changes
Here's the wf function I was talking about which does this:
https://github.com/Wikia/app/blob/dev/includes/wikia/GlobalFunctions.php#L1722-L1727