New home page

[micahilbery]

Things still needed:

• [ ] links for "See Compatibility", "open source", "Mozilla"
• [ ] Download buttons in nav, header, and "Free Your Inbox" section

[micahilbery]

[ryanleesipes]

On links:

Let's kill "See Compatibility" for now (comment it out or something). "Open Source" can link to this page: https://en.wikipedia.org/wiki/Open-source_software

Mozilla can link to https://mozilla.org

[ryanleesipes]

Perfect, thank you @micahilbery

[Sancus]

I'm going to merge this as-is so I can get started on translations, please do a followup.