[READY] Cleaning codebase

# tl;dr 

Removing some code which is not useful anymore thanks to the latest merges in `refactoring-base`.

# What has been done

-  removing the `$` variable
- RAF isolation (to avoid a global override and possibly causing side effects in people's code)
- `cache` removal

This last part needs to get attention. While cleaning it I wondered why a `replaceChild` occurred systematically in `replaceImagesBasedOnScreenDimensions`. I considered this part should just have to update the placeholder `src` attribute.

Useless things can be removed by discarding some commits, I tried to make them releventelly atomic :-)

![](http://i.imgur.com/nsHeZkf.gif)