76 whitespace and more

- This PR resolves #76 
- This PR should conform to our prescribed feature-branch > rebase > PR workflow.
- The primary change here is a restructuring of the markup on index.erb. We now have a more semantic and granular page structure, which moves us in the direction of more flexible and nuanced styling.
- Via the improved markup, we've added quite a bit of additional whitespace between form elements. This will help with scanning the form visually.
- We've upped the typography size in a few places, and refined the typographic hierarchy.
- Perhaps most noticeably, the title and subhead are now visually and structurally discrete from the form itself, evidenced primarily by a full-width blue background and off-white text.
- These styles are not meant to be indicative of a long-term direction, but rather to improve the experience for 7/30/2014.