Code Demo design

This is laying the ground work for the home page code demo where a user can paste code and it will show up as parsed by Rouge. Also:

* Added guard config to speed up testing workflow
* Added simple_form initializer so it would stop complaining
* Made the default language Ruby (can be selected of course)
* [i18n-tasks](https://github.com/glebm/i18n-tasks) was complaining about a missing title translation even though it's there. It's a [known bug](https://github.com/glebm/i18n-tasks/issues/98), but the way to fix it is to ignore whatever can't be parsed

@jneen I'm planning to work on the parser next. I'm thinking it will call asynchronously to a ParsesController and return HTML to put in the `div#formatted`. Thoughts?