Polish landing page links, hero, and hover effect

* Update copy in introduction
* Improve color of hover links
* Add color and animation to global nav hover
Use waypoints to animate global nav

* Resolve merge style conflicts
* Refactor JS with data-attributes
* Make comments after PR review
Resolve Safari SVG rendering

* Remove old Middleman brand assets
* Move `middleman-logo.svg` outside of `logos/`
* Modify box-shadow value of global nav style

https://trello.com/c/YdBlvKwh