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 
No, it should... Let's keep it in for now, while we set stuff up. How do I add that, just create a page_events, or are you OK making a super simple skeleton? I have text to fill it with... Should I make an issue?