ImageFaceCrop needs to go into bob.bio.face

Irrespective of the fact why another face cropper is needed here: https://gitlab.idiap.ch/bob/bob.pad.face/blob/b0a14393f109e8bc15928ade60b0614e34e4b73f/bob/pad/face/preprocessor/ImageFaceCrop.py, this is a face cropper and it is useful for others too. The best place for it is hence a bob.ip... package or bob.bio.face where all our face croppers are. When it is moved to bob.bio.face, you can also get feedback from me or @mguenther, or @andre.anjos to see if this class is actually needed. Then, if needed, we can merge it in bob.bio.face.