Separate Vendor Bundle

This pulls all the vendor libs into their own bundle, leaving the app bundle lean and very quick to regenerate.

To add a new library to the vendor bundle, add it to the "libs" var in "gulp/vendor.js":

```
var libs = [
   'backbone',
   'clientconfig',
   'crossing',
   'fastclick',
   'in-viewport',
   'jquery',
   'loglevel',
   'MD5',
   'react',
   'react/lib/ReactCSSTransitionGroup',
   'react/lib/cx',
   'rsvp',
   'underscore',
 ];
```

Anything not added to the vendor bundle will simply be included in the app bundle.