COMP: Ensure FindDCMTK module works with and without DCMTKConfig.cmake file

In the case the provided DCMTK build or install tree doesn't have a
DCMTKConfig.cmake file, the first call to "find_package" should fail
quietly so that it doesn't prevent the rest of discovery process from working
as expected.

See #329
Added skeleton for ctkDICOMDatabase::updateDisplayedFields
Input data assembled and passed to the displayed field generator (not tested)
Merge remote-tracking branch 'remotes/lassoan/276-dicom-database-display-tables' into 276-dicom-database-display-tables

Conflicts:
	Libs/DICOM/Core/ctkDICOMDatabase.cpp
	Libs/DICOM/Core/ctkDICOMIndexer.cpp
	Utilities/CMake/FindDCMTK.cmake