Add color to `x minutes ago` in activity feed

We should try to avoid introducing another skinning value and find a way in which we can piggyback on a different skinning value

![screen shot 2013-10-09 at 13 49 25](https://f.cloud.github.com/assets/109850/1297396/4431af66-30e1-11e3-9ee9-9d363dd65bca.png)