WIP: DO NOT MERGE: Crop faces according to pose

Hey @tiago.pereira @amohammadi

I made a script to crop faces and cluster them according to pose ... It's not that generic (and the cropped image size and eyes/mouth position are hardcoded for the moment), but I still think it's worth to put that into the master.

I plan to rework on it and make it more generic, i.e. allowing to specify the cropped size and inferring eyes and mouth position automatically based on anthropometry.