Updated front page

I never was quite happy with the design of the front page. This update should provide a fresh look that would perhaps fit in nicely with @pekrau's efforts to bring some structure to how we work with open source development at SciLifeLab.

I'm still very much not sure what the execs will say about the re-use of the SciLifeLab logo so this should be seen as a humble suggestion.

This is what the site could look like:
![screen shot 2014-11-28 at 10 56 38](https://cloud.githubusercontent.com/assets/1220232/5226267/4c9e53f4-76ed-11e4-9c48-cca84706dc8c.png)