ENH - matlab code; build in support for multiframe dicom files

[schoffelen]

This is a long shot, and feel free to ignore, but this PR implements support for multiframe dicoms in the matlab reader.

Context: the Siemens Skyra scanner at the Donders Institute now natively creates multiframe dicoms since a recent software update. Our FieldTrip code (https://github.com/fieldtrip/fieldtrip) relies on load_dicom_fl.m for the reading of dicom anatomical volumes. Given the different formatting of the header (and data) this now fails for obvious reasons.

I could easily implement a workaround that does not touch freesurfer functions, but on the off chance that you find this addition useful, I still submit it here, realizing that:

• the matlab code probably does not have the focus of attention of the developers
• core functionality (e.g. mri_convert) does not seem to support multiframe dicoms, so it could have been a conscious design choice not to support this particular file format (although I couldn't find anything about this when doing a shallow online search)
• I only tested the changed code on a few files that were collected at the Donders Institute, so I don't know how robust it is

[schoffelen]

Hello, is there anything related to this PR which prevents it from being picked up by the developers?