Splash page redesign

@jlord and I have been working on a lightweight redesign to give the splash page a bit of :heart:. Here's our thinking:

1. By far, the most common questions asked by government employees is "What is GitHub" and "how would my organization use it", two questions the site didn't do a really great job of answering ([What is GitHub?](https://government.github.com/about/) is buried several clicks in). Let's answer that :question: right up front and center.

2. A clear call to action: the site as currently laid out doesn't have a clean flow for "first steps". How do I sign up? What's the first thing I should do? How do I get help? What do I do if I have a question? We should be proving clear outs for: 1. Creating an account, 2. joining the best-practices peer group, 3. creating a government organization, and 4. getting in touch with a human if you have any questions.

3. The stories are proving difficult to collect, and based on our experience, don't serve as a strong motivating force. Nobody says "oh I saw that story on government.github.com and then decided to open source X". Those case studies can be better curated within the `/government/best-practices` community, where government employees are able to speak a bit more casually.

Not to mention, @jlord worked her :art: magic and made things absolutely :sparkles: (dat seal!). A little added color and pop to give the content the presentation it deserves.

## Todo

- [ ] Polish copy
- [ ] Transfer stories, FAQ, and project ideas to https://github.com/government/best-practices
- [ ] Set up redirects for existing story links
- [ ] In a separate iteration, optimize the org logos loading, potentially using a sprite and single image

## Here's what it looks like

![gov github com](https://cloud.githubusercontent.com/assets/282759/3725766/410b3014-168c-11e4-8530-a8cd822ea4ff.png)