Included broccoli-asset-rev for fingerprinting in EmberApp

I have included https://github.com/rickharrison/broccoli-asset-rev to both fingerprint files as well as replace them in the source. This will turn:

`<script src="assets/appname.js"></script>`

into

`<script src="assets/appname-ce5adb2fb916f0fdaa16c282dd074239.js"></script>`

I added an option to EmberApp to pass strings for excluding files to be fingerprinted. `EmberApp.options.fingerprint.exclude` should be an array of strings, which if any file contains any string in that array, it will not be fingerprinted. As an example, I do not fingerprint my typography.com stylesheets.

Also, there is a `prepend` option, which is an object which pairs the current env to a string to add to all of the asset filenames.

```
var app = new EmberApp({
  name: require('./package.json').name,

  minifyCSS: {
    enabled: true,
    options: {}
  },

  fingerprint: {
    exclude: ['fonts/169929'],
    prepend: 'https://subdomain.cloudfront.net/'
  },

  getEnvJSON: require('./config/environment')
});
```

If a prepend string is specified, it will be added in front of all of the fingerprinted assets. This allows for easy CDN addition to assets.

From

`background: url('/images/foo.png');`

to

`background: url('https://subdomain.cloudfront.net/images/foo-735d6c098496507e26bb40ecc8c1394d.png');`

Let me know what you think and I can improve upon it!