Create separate sponsor page.

[emstanley]

Instead of having a sponsors section on the home page. We're going to have a separate sponsor view/ page and add the page as a top menu item.

We now have an API endpoint for sponsors. See this issue for details: #16

Each sponsor image is clickable and navigates to a URL specified by our sponsor contact.

The sponsor page will look much like the sponsor section from this year. The sponsors will be displayed by sponsor tier, with the "Become a Sponsor" call to action at the bottom of the page.