V2.4.0

Release branch for v2.4.0

Currently this consists of:
* New styling for Featured Content in the default ContentView template and stylesheet.

It will also have the following performance improvements for ContentListView:
* Lists will no longer grow unbounded as things stream in. Once a large amount of items are rendered, the oldest ones will start being removed from the DOM, and inserted back behind the "Show More" button.
* ContentListViews will have an awesome new animation when Content is added

[streamhub-wall](https://github.com/Livefyre/streamhub-wall) will be updated soon after with some exciting updates, including some big performance wins.