Update About page styles

References #3568 & #3575

With the move to new global styles, the about page styles got a bit borked. This fixes those.
It also adds hover styling to nicely show contributor names, from [this comment](https://github.com/TryGhost/Ghost/pull/3575#issuecomment-53723235) and the below gif.

![contribs](https://cloud.githubusercontent.com/assets/390392/4108896/5aedba0c-31de-11e4-9f4d-a95621a3fbbc.gif)