Add the ability to recursively collapse nested directories

The intended outcome is to be able use `alt-ctrl-[` or `alt-left` to collapse a directory, and all expanded directories nested below it.

I'm fairly new to this stuff (Atom, coffeescript, test-driven javascript, and oss in general), so I'd love some feedback.

Also, it would be nice to be able to `alt-click` and produce the same behavior, but I'm not quite sure how the click events work.

![tree-view2](https://f.cloud.github.com/assets/599209/2416971/0a8331c6-ab12-11e3-9d5b-4f6894e733f0.gif)