#CT-7653: Remove scrollbar from iFrames that extend past lenght of page

@pheuter I want to get your feedback on my changes before we merge. See comments.
Right now, `scroll` will always be falsy because you need to pass it in to the construct via [addWidget](https://github.com/CrowdTwist/widgets-js-sdk/blob/4ad15eed38a93d71b2e6c6d4a47747a5ca2c7640/src/widget.coffee#L134) method that calls the constructor.