Update FindDCMTK.cmake module to support NO_MODULE mode

This will allow to build CTK against the patched-3 branch available on
github.com/commontk/DCMTK [1]

[1] https://github.com/commontk/DCMTK/tree/patched-3

Contributed-by: Kent Williams <norman-k-williams@uiowa.edu>
Merge branch 'update-find-dcmtk-to-support-no-module'

* update-find-dcmtk-to-support-no-module:
  Update FindDCMTK.cmake module to support NO_MODULE mode