New Homepage

This PR documents the creation of new homepage according to the mock shared via email.
Also tweaked the styling for sign up page.
Great question Nikil! That interaction is something I've considered. But the removal of the back button is deliberate. Here's the reason why: the only thing that button does is go back to the homepage, which the browser UI already does. It's placed near the top left corner as well, where the browser UI anyway. Putting is there is simply adding clutter and UX redundancy to the page. 

You do bring up a good point in that it's generally good practice to NOT force the user to press the browser back. But like most rules though, the context determines how the rule is applied. In this case, there are only two reason people will click on the signup button: A. You're there to sign up, or, B. clicked there by accident. If you're B, then you would use the browser back button more likely. If you're A though, we shouldn't remind you to abandon your signup process.

I think these are the reasons why this is a common UX feature for signup pages. Case in point in Erik's example above. If my memory serves me correctly, I think Habitat also doesn't have a return to home button.