Reportback form cropping

This is a pull request for updated report back cropping functionality. Hoping to get something up on staging so people can start testing. Fenders - let me know what you think of the js structure. I would love to sit down and go over it at some point to see if this is the best approach for us. 

@aaronschachter @DFurnes @weerd cc/ @barryclark 
Is there a reason you're applying the `position: relative` here rather than in the stylesheet?