Add support for Secondary Capture radiographs

[zgypa]

As needed by BBGSC, we need to store scanned film radiographs of various anatomical regions. Probable route would be:

• Secondary Capture IOD
• RG Modality
• Anatomic Region Sequence to distinguish the various types

How about having pydicom templates which can be extended? So a generic class for

• SecondaryCapture.RG
  • SecondaryCapture.RG.LL
  • SecondaryCapture.RG.PA
  • SecondaryCapture.RG.HW (Hand/wrist)
  • etc.

Then use that class, and change UUIDs, dates, Age, PatientID only as appropriate, and done!