Homepage refactor

There's definitely some visual tweaking and cleanup that needs to be done, but after dropping the new header nav in, I decided to go ahead and get the ball rolling on this.

To view this, you should be able to pull the `new-header` branch down from the Github app, then switch to that branch and view it locally in your browser. I can help you in person if that doesn't work.

Things to note:
- The hamburger menu only shows when the viewport is less than 768px and the other header nav hides. Let me know how you want to style the nav links inside the basement though.
- I removed the slider js – I can add that functionality back in, but I need new hero images, and it's probably easier to talk about in person.
- I removed the gray bar with the down arrow under the hero. I'm not sure if that's something you wanted to keep, but it should be easy to add that back in.
- The typography, spacing and mobile styles are a bit different in the value props section. This probably needs the most attention visually, but tried to keep it within the system of font-sizes, colors, and fonts in the issue.
- I adjusted the value props section svg images to all be the same dimensions and just went with my gut for sizing.
- The *Shop is now open* link uses the same style as other white links and has a gold hover state. We can add a new style if you want white links without hover states.
- The Mail Club footer section goes full-width, like the issue. It used to be contained with a max-width.
- I changed the way the responsive type scale works, and there are a few issues with font-sizes. I'll try to clean that up before you see it, but let me know if anything looks off.

Still to do:
- [ ] Add hex value for gold button hover state and transition
- [x] Add automatic slideshow for hero section (if you still want that)
- [ ] ???