Video download via proxy

This pull request adds a quick n' simple proxy download option to the script. The feature may come in handy for those sssssuffering behind internet censorship or a firewall.  

Ideally the script should download the file and serve it from the server itself regarding a higher transfer speed. Also it's possible to fetch the video title and its size for a better download experience which all in all, I was too lazy to implement :)

Please let me know what you think.