Move organizations to _data directory

[XhmikosR]

https://github.com/mojombo/jekyll/blob/master/site/docs/datafiles.md

This seems like a more flexible solution for government.github.com compared to having to edit _config.yml which is becoming huge anyway.

Maybe having a yml file for each country would make the situation much cleaner.

[nschonni]

Related to #139 and #75

[benbalter]

The feature's not yet stable, let alone on Pages, but something to discuss depending on the outcome of #75. Biggest pushback would be complexity.

[XhmikosR]

@benbalter: I didn't notice this was a new feature to be honest. But it does sound like the best compromise for government.github.com. I guess we should wait a little bit more. :)