Update gdcm dicom library for Python 3.8

[Tom Goddard]

Currently gdcm (grassroots dicom library) is not being installed in the ChimeraX daily builds since I updated to Python 3.8 a few days ago. Unfortunately gdcm does not have any packaged Python 3 releases so it is pretty painful to create versions for ChimeraX. And it turns out that it was not working in ChimeraX 1.0 and 1.1 because of a missing openjpeg library, but did work in ChimeraX 0.92 at least on my machine. This library allows opening lossless 16-bit jpeg DICOM files often used for clinical imaging and not handled by PIL or PyDicom.

The gdcm 3.0.8 releases at github use Python 3.8 and are a starting point for making a ChimeraX prereq installation.

[Tom Goddard]

More details about my progress using gdcm 3.0.8 and fixing wrong library paths are in comments at the end of ticket #1745

[Tom Goddard]

This gdcm package was needed in the past to open lossless 16-bit jpeg. If a user gives us an example DICOM file using this format this might be worth fixing. I have an example file somewhere but no-one has complained about it not working the past few years, probably because almost no-one has tried DICOM in ChimeraX. So we should work on getting more users by promoting DICOM before working on obscure limitations like this one.

[Tom Goddard]

Ticket #1745 is the kind of error that is thrown trying to open a lossless jpeg dicom.

[Tom Goddard]

There is an example lossless jpeg DICOM file attached to ticket #1745.

[Zach Pearson]

(Same resolution as #1745) Added python-gdcm==3.0.12 to app_requirements.txt