Add more OEmbed providers, and support for noembed.com

This pull adds support for:

* flic.kr
* gist.github.com
* mobypicture / moby.to
* polldaddy,
* scribd.com
* slidesha.re
* speakerdesk
* yfrog

These services were found via the WordPress 3.5.1 source code, embedly provider list, and some educated guesses.

The second commit add support for http://noembed.com, a free service which - like embed.ly - also supports several popular sites that don't support oembed themselves.

I hope you can merge this patch, so these improvements can find their way into a new micawber release :)