collection and shelf detail previews (bug 1035445)

![](http://f.cl.ly/items/1s3S0W3V1G382k3X1M2H/Image%202014-07-17%20at%204.13.36%20PM.png)
For the record there's nothing about this that I like or agree with.
Hm, can we not hardcode this in? 

With @chuckharmston's stuff, there will be two previews, one for feed and one for feed detail (below the fold). We should show a complete rendering of the feed homepage representation, and a complete rendering of the feed detail representation.

I would modify feed_previews.js to render it twice for shelves + collections, one where we don't pass in an ```is_landing``` context and one where we do pass in an ```is_landing``` context var.