ENH: Added python utilities that download, unzip, import, and load DI…
…COM data
New context called OnlineDICOMData was added in DICOMUtils that does the following:
- Download zip file from URL
- Unzip file to specified directory
- Import the unzipped DICOM files into the database
- Load only just imported files into Slicer, with the option of verifying the selected DICOM plugins and the number of loaded nodes of given types
SubjectHierarchyGenericSelfTest updated to use this new context