Preprocessor refactoring, VideoFaceCrop+ImageFaceCrop replaced with FaceCropAlign+Wrapper

This MR is the refactoring of the face cropping preprocessor. Two tasks are addressed:

1. First, the combination of two classes VideoFaceCrop + ImageFaceCrop simplified to a single class namely FaceCropAlign. This class can now be used with a Wrapper of bob.bio.video.preprocessor . An example of how to use the class with Wrapper: https://gitlab.idiap.ch/bob/bob.pad.face/blob/preproc_refactor/bob/pad/face/config/lbp_svm.py

2. FaceCropAlign now also supports facial alignment, based on the positions of the eyes.

@ageorge and @kkotwal , can be useful for you.