Support Direct HTTP(s) Stream Links

[jaruba]

We should allow users to add direct HTTP(s) stream links too that don't require any type of extraction (such as youtube-dl).

This would allow users to save different video / audio links they find online in their library. Useful, one example: radio station links

References:

• https://github.com/jaruba/PowderWeb/issues/25
• http://dir.xiph.org/yp.xml (icecast stations directory, all are direct http links)
• http://directory.shoutcast.com/ (shoutcast stations directory, all are direct http links)
• http://www.radio-browser.info/webservice (api for radios, might be useful later on though)