Cockpit website: redesign & new content

[Garrett LeSage]

Hi all,

I've spent a little time this week here and there restyling the Cockpit 
website and working on new content for the front page.

Preview: https://garrett.github.io/cockpit-project.github.io/

The goals:

1. Improve the messaging on what Cockpit is, can do, and why someone 
would want to use it
2. Give the site a fresh look

Anyway, the above link addresses these points. There still are a few 
very minor rough edges on the implementation (guide and mobile tweaks) 
and the content could use some editing too... but it's ready for feedback.

What do you think?

Please respond on the pull requests:

- restyle: 
https://github.com/cockpit-project/cockpit-project.github.io/pull/194
- content: 
https://github.com/cockpit-project/cockpit-project.github.io/pull/195

I'll be away on PTO for the next two weeks, but I'll take feedback into 
consideration and make adjustments accordingly.

Cheers,
Garrett