allow for op shelf landing images (bug 1067432)

This will require a sync of `feed_item.html` from fireplace in order to see the landing preview properly.

![](http://f.cl.ly/items/2N103N2D1R45261C1R0V/Image%202014-09-17%20at%203.26.06%20AM.png)
Don't know if we can make the error key match the landing field.