Add DCMTK 3.6.0 support to CTK application.

Since the ctkDICOMUtil method have been updated in commit 12c052f to work
with DCMTK 3.6.0, this commit update the application code to use it.

See #405
Merge branch '405-support-dcmtk-360'

* 405-support-dcmtk-360:
  Add DCMTK 3.6.0 support to CTK application.