COMP: Use portable method to find source dir & find DCMTK headers

Change-Id: I28bce754947efa74b09d7ba7f478443378c89ed0
COMP: Start using ITKConsortium github to retrieve DCMTK.

Change-Id: I078b5374b9b66a7d4cc2a4c4030a911f1be4e8aa
Merge topic 'USE_SYSTEM_DCMTK_FIX'

ebcceac COMP: Use portable method to find source dir & find DCMTK headers
Merge topic 'USE_ITKConsortium_Githug_Repo_DCMTK'

83e6649 COMP: Start using ITKConsortium github to retrieve DCMTK.