Change how active matches are shown in project page

![screen shot 2014-07-30 at 2 53 47 pm](https://cloud.githubusercontent.com/assets/667753/3753488/8615cb6a-1812-11e4-9f5b-0c1473eb92c2.png)

Implements #408.

/cc @snconnolly
It is used to flag values expecting HTML content (thus automatically calling `#html_safe` in `I18n.translate` helper).

http://edgeguides.rubyonrails.org/i18n.html#using-safe-html-translations