@mzikherman: Wire up Gemini uploading for thumbnails & scatter brained stuff

Sorry for the large PR (FWIW most of the line number diff is a new shrinkwrap).

What this PR mainly does is use this little [gemup](http://github.com/artsy/gemup) module I wrote for Gemini upload. This module is a lighter alternative to [the artsy-gemini-upload plugin](https://github.com/artsy/artsy-gemini-upload) by allowing interaction with File objects directly & no dependency on existing DOM or the jquery.fileupload plugin (at the cost of rolling your own UI bits/lack of other solved problems you get with jquery.fileupload). In my case I'm going to often want "lower-level" control of the upload process so I thought it would be nice to provide a smaller wrapper over the ajax parts of uploading through Gemini.

Sorry for the scattered-brained extras here, but also included is:
* API is more flexible about blank values
* Sort articles by "most recent" by default `updated_at: -1`
* Filled out "thumbnail view" UI (including gemup-backed thumbnail upload)
* Split up article layout views into EditHeader/EditThumbnail/EditView

![image](https://cloud.githubusercontent.com/assets/555859/4620250/cf405684-531d-11e4-8d63-dceb6ed664d4.png)