Facia hover states

These aren't amazing but they're probably better than what we have (also they match up with buttons and other parts of the site fading slightly darker on hover).

![screen recording 2014-11-05 at 12 50 pm](https://cloud.githubusercontent.com/assets/1607666/4917866/8425d7ee-64ea-11e4-9800-b3b472d544c5.gif)

This also adds a placeholder image as a result of the transition, which we wanted to add on mobile for when images were loading in.

![screen shot 2014-11-05 at 12 52 20](https://cloud.githubusercontent.com/assets/1607666/4917872/99415cac-64ea-11e4-981c-cc8a2fb3ce98.png)
Is the element selector necessary here?