Add a globe and rework the rest

This brings a small locator globe to the lower right corner.

Before:
![before](https://cloud.githubusercontent.com/assets/41094/5059633/11964502-6cd7-11e4-9107-4b06f0ba47e9.png)

After:
![after](https://cloud.githubusercontent.com/assets/41094/5059635/3ee65d1c-6cd7-11e4-8508-920c724425e2.png)

When you click on the globe, a new image loads.  We can alter the styling of the globe as we like.

Other changes unrelated to the globe:
 * removed unused css classes and style blocks (stuff for IE, Opera, etc.)
 * simplified the markup and style
 * made the scene fade in on load
 * added a link to the related gallery post

This branch includes an Atom feed for Gallery entries.  When planetlabs/planet.com#115 is merged and deployed, we can remove `data/gallery-atom.xml`.