Extract thumbnails.
Make SoundcloudSetIE a subclass of SoundcloudIE to reuse some code.
Directly extract the file url without downloading an extra page.
Now it downloads the video over http in one file, it doesn't downloads in fragments
Added a test and use the methods in InfoExtractor for downloading webpages
The new extractor and YoutubeSubscriptionsIE are subclasses of YoutubeFeedsInfoExtractor, which allows to fetch videos from http://www.youtube.com/feed_ajax