Add support for MediaCrush titles and descriptions

![2014-12-10_19 23 27](https://cloud.githubusercontent.com/assets/1310872/5388084/0ffc08ce-80a2-11e4-9e20-40b4ecd96b10.png)

![2014-12-10_19 23 57](https://cloud.githubusercontent.com/assets/1310872/5388088/1eb7338e-80a2-11e4-8f4e-5853132d4d55.png)

![2014-12-10_19 24 04](https://cloud.githubusercontent.com/assets/1310872/5388089/2120c84c-80a2-11e4-9350-c4a759667bf6.png)

This pull request also makes some other minor changes:

* Use the "video-muted" expando class when "has_audio" is false on a MediaCrush link
* Expand MediaCrush links on "view images" if "has_audio" is false