[ENHANCEMENT] added ability to opt out of including jQuery in vendor.js

You can remove jQuery form the vendor.js file by adding  `includeJquery: false` to your brocfile.js

We are loading our ember app into a page that has jquery already loaded in the page. We don't want to add it twice. 

```js
var app = new EmberApp({
  name: require('./package.json').name,

  includeJquery: false,

  getEnvJSON: require('./config/environment')
});
```


Cheers for all the hard work.