New `highdicom` python library

Good news for dicom developers: a new python library for has just been made public under the MIT license for multiframes, segmentation, reporting, and related topics. It can be pip_installed into the Slicer nightly if you want to try it out. Longer term we can discuss how best to make use of it in Slicer, and potentially we can factor out some of the dicom code currently in Slicer’s DICOMPlugins for this package.