Changing splash logo

Responding to issue raised by Julien.

![screenshot 2014-12-05 12 08 05](https://cloud.githubusercontent.com/assets/29096/5319445/6bac17a6-7c77-11e4-891d-636da19077be.png)

You are correct, width: 19.5176rem; would be the right aspect ration dimensions, but since the SVG is the background: URL...; of the containing anchor, with backgrond-position: center center;, and background-size: contain;, the SVG scales to fit the tightest dimension of the container, instead of distorting the image.