Add `new folder` button to save as menu

![new-folder mov](https://cloud.githubusercontent.com/assets/986404/5591079/4c3384b4-9116-11e4-9de3-23d499094496.gif)

This is a minimum UI, and probably not ideal.  Might be best to have @bradicdesign take a look at this feature as I didn't want to make too many design decisions.