Add a comment component for nits

This adds a new component called `comment` to the styleguide and uses it for the nit layout. This is just a suggestion but it would also fix #1692. It should be reused wherever we have a discussion stream (i think right now there are just the nits, aren't they?).

![bildschirmfoto 2014-11-22 um 22 26 26](https://cloud.githubusercontent.com/assets/5362483/5155756/d5ee1334-7296-11e4-8564-6ab8d7fa5420.PNG)

![bildschirmfoto 2014-11-22 um 22 26 49](https://cloud.githubusercontent.com/assets/5362483/5155757/dd3dd5d4-7296-11e4-9b0d-dc161ff455cd.PNG)