Since 07cc454 (ie the switch to Meteor 1.2) we includes the `es5-shim`
polyfill to support methods like `Array.prototype.forEach` in a
consistent way across all supported browsers (IE8+).
MDG recently released a blog post recommending the use of these native
methods instead of underscore [0]. We know follow this recommendation.
This commit also favor some ES6 features (argument defaults,
destructing assignment) in places where we didn’t use them.
[0]: http://info.meteor.com/blog/es2015-get-started
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