Initial preparations for i18n

This pull request is, of course, not ready to be merged. It is meant to restart the conversation around translating the site and to ask for feedback on the work I've been doing.

Using the default rails way of internationalizing an app poses a few challenges, specially when we have large static files. 

Simpler files like the [homepage](https://github.com/DiogoAndre/gitscm-next/blob/i18n/app/views/site/index.html.haml) are easy to process, and the [resulting yaml file](https://github.com/DiogoAndre/gitscm-next/blob/i18n/config/locales/en/views/site/index.yml) look relatively neat. Things are totally different with long files like the [svn crash course](https://github.com/DiogoAndre/gitscm-next/blob/i18n/app/views/site/svn.html.erb), and the [associated yaml file](https://github.com/DiogoAndre/gitscm-next/blob/i18n/config/locales/en/views/site/svn.yml), which is long and a bit confusing.

YAML files may not be too inviting for people willing to help translate the site, but maybe it can serve as a starting point for a more user-friendly method for translating the content. I'm thinking on something similar to [Amara](http://amara.org/), the service GitHub is using to crowd-source the [translation of GitHub's videos](http://amara.org/en/teams/github/).

I think it is also worth mentioning that I already have most of the content [translated to Brazilian Portuguese ](https://github.com/DiogoAndre/gitscm-next/tree/pt-br). So, when we get the i18n infrastructure ready, we'll have at least one language to show off! 

Please, share your comments! Be honest, but be gentle. ;-)