Adds URL to look up JSON-formatted sponsor listing.

Similar to the existing schedule JSON dump, it would be helpful
to have a way to get all the sponsor information programmatically.
This allows for easier updates to e.g. the mobile app when sponsor
info changes.
Merge remote-tracking branch 'felixc/sponsor-json' into pyconca2013
Removes extra utf-8 stuff. See #109.
Returns None when sponsor benefits don't exist or are not active. See #109.