update and re-arrange contribute page

Ok, I've fully re-factored the contribute page. The features for 7 page was my inspiration. It has a few layout issues, I hope somebody can fix them - I couldn't. Otherwise, there is still room for improvement but it is far better than the current one so I'm for merging already!

@karlitschek @tomneedham @jancborchardt 
< ul > Is 'unordered list'. It should be this tag that is changed, to < ol > and numbers will magically appear instead of bullets :)