From #11: new field image_orientation

[yarikoptic]

As briefly discussed and agreed in rordenlab/dcm2niix#153, BIDS2NDA should acquire super-powers to deduce now required values of image_orientation expressed in 3 possible values: Axial, Coronal, Saggital.
DICOM has no direct knowledge about that. BUT we have ImageOrientationPatientDICOM filled with DICOM vectors from tag (0020,0037) .
@matthew-brett - given your extended knowledge on the subject (http://nipy.org/nibabel/dicom/dicom_orientation.html) - do you see an obvious code to implement such guesswork?