Rough draft of a new homepage; #1074

We've talked a lot about different ways to make the homepage dynamic.
Here I'm taking the opposite approach: this homepage is designed to
function primarily as a first impression of Gittip that answers the most
basic questions, and then leads people in one of three further
directions: signing up, browsing communities, or reading about Gittip.
Let's make the community and profile pages the focus of dynamic activity
on the site, not the homepage.
Use a single penny bg + color overlays

This ensures that pennies line up from block to block.
Merge branch 'master' into new-homepage
Shelve
Merge branch 'master' into new-homepage
Homepage is pretty presentable. Homestretch!
Make new homepage responsive
Tweak verbiage for browsing communities
Responsiveness tweaks
Fix up test suite
Merge branch 'master' into new-homepage
Tweak site description in a couple places

Use the verbiage we're now using on the homepage.
Remove old thing from homepage
Fix sign-in on inside pages
Here's a very basic authenticated homepage
Redirect to profile page from homepage sign-in

`/about/me//` is a hack to work around bugs in Aspen wildfile handling.
Prune an extra CSS definition
Fix homepage on Firefox
Add Sign Out link on authenticated homepage
Make sign out link parallel to other links