Tap image for zoomable view - Like in Paper

Hi,

I have worked on your repo and added the functionality where the user can tap the motion view and transition to a zoomable one. Like it is done in the Paper app.
I have added some customization so you can enable or not this functionality. 

Also this interaction creates a complete independent view for zooming. Therefore not messing with the original MotionView.

Hope you will find this interesting and worth pulling ;)

Let me know if you merge and update your cocoapods so I can use it :) !

Tanguy