Gallery most popular container

This PR introduces a new gallery container which uses the "news/auto" pattern and is currently powered by a simple lookup against our most popular agent filtered by content type.

- Gallery most popular controller
- Gallery container
- Styles for container
- Refactor icon and styles for global gallery item
- JavaScript to transclude onto gallery page

![safari](https://cloud.githubusercontent.com/assets/80089/4197901/3ca24eb4-37f1-11e4-8c67-017ac7d0b77c.png)

/cc @mattosborn @rich-nguyen