PEP code cleanups in providers.py
Add new providers discovered via Embedly/WordPress and some good guesses..

This adds:

* flic.kr
* gist.github.com
* mobypicture / moby.to
* polldaddy,
* scribd.com
* slidesha.re
* speakerdesk
* yfrog
Add support for Noembed.com, via bootstrap_noembed() function

This a free service which also implements support for non-oembed sites,
however it doesn't support as much as Embed.ly does.