PLATFORM-654: get data from ResourceTiming

Aggregate it and send it via Bucky on:

* DOMReady
* window.load
* 5 seconds after window.load

[Supported desktop browsers](http://caniuse.com/#feat=resource-timing): IE10+, Fx 34+, Chrome 31+ and Opera 26+

@wladekb - this PR is for code review purpose. Please **do not merge**!