Bug 1100915 - [Usage][Refactoring] Use LazyLoader to load views. r=salva

> Good test but I would prefer to split into several cases. 

I don't mind, I can divide it into two separate tests:
* One that checks that resources are successfully inserted into head. Not sure though what you meant by "it suffices asserting parent is head"? If you meant that we can check ```styleNode.parentNode === document.head``` where ```styleNode``` is style node from template then it wouldn't work because you create another node inside LazyLoader callback. Btw, I don't really understand why we can't just _move_ that node to the head, but it's out of scope of this patch anyway :)

* One that checks for duplicated styles.

> And I'm wondering if activation is even needed as you can put scripts and links where you want and they should be interpreted by the moment they are in the DOM. Can you try removing activation code to see what happens?

I believe that HTML5 doesn't allow executing scripts inserted via ```innerHTML```:

```script elements inserted using innerHTML do not execute when they are inserted.``` [1]

[1] http://www.w3.org/TR/2008/WD-html5-20080610/dom.html#innerhtml0