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

![google chrome](https://cloud.githubusercontent.com/assets/80089/4165316/d8003a86-3500-11e4-9373-06e2f521ecb3.png)


/cc @mattosborn @rich-nguyen 
caching?