Allow for lack of ImageOrientationPatientDICOM

[dasturge]

ImageOrientationPatientDICOM and InPlanePhaseEncodingDirectionDICOM are used in conjunction to get the readout direction of a subject.

These are probably exclusively put in by dcm2bids, and we should allow for two cases:

one, change the logic in the pipeline so these fields are only used when a fieldmap is present.
two, allow for an explicit readout direction input, as in the original HCP bids application.