FindDCMTK - Do not explicitly set DCMTK_DEFINITIONS

Following commit commontk/CTK@12c052 fixing a packaging Debian bug,
the DCMTK_DEFINITIONS was set directly inside the FindDCMTK.cmake
module using "add_definitions".

When used outside of this project, setting automatically the definition
could have some unintended effects. For example, by globally adding
DCMTK_DEFINITIONS (and more specifically HAVE_CONFIG_H), it prevented from
compiling successfully program against the "tclap" library. Compile errors
like the following occurred:

// ------------------
In file included from <DIR>/SlicerExecutionModel/tclap/include/tclap/CmdLine.h:27:0,
                 from <DIR>/Slicer-build/Modules/CLI/CheckerBoardFilter/CheckerBoardFilterCLP.h:13,
                 from <SRC>/Modules/CLI/CheckerBoardFilter/CheckerBoardFilter.cxx:23:
<DIR>/SlicerExecutionModel/tclap/include/tclap/MultiSwitchArg.h:44:2: error: #error "Need a stringstream (sstream or strstream) to compile!"
 #error "Need a stringstream (sstream or strstream) to compile!"
  ^
<DIR>/SlicerExecutionModel/tclap/include/tclap/MultiSwitchArg.h:171:2: error: #error "Need a stringstream (sstream or strstream) to compile!"
 #error "Need a stringstream (sstream or strstream) to compile!"
  ^
In file included from <DIR>/SlicerExecutionModel/tclap/include/tclap/UnlabeledValueArg.h:30:0,
                 from <DIR>/SlicerExecutionModel/tclap/include/tclap/CmdLine.h:28,
                 from <DIR>/Slicer-build/Modules/CLI/CheckerBoardFilter/CheckerBoardFilterCLP.h:13,
                 from <SRC>/Modules/CLI/CheckerBoardFilter/CheckerBoardFilter.cxx:23:
<DIR>/SlicerExecutionModel/tclap/include/tclap/ValueArg.h:43:2: error: #error "Need a stringstream (sstream or strstream) to compile!"
 #error "Need a stringstream (sstream or strstream) to compile!"
  ^
<DIR>/SlicerExecutionModel/tclap/include/tclap/ValueArg.h:97:2: error: #error "Need a stringstream (sstream or strstream) to compile!"
 #error "Need a stringstream (sstream or strstream) to compile!"
  ^
// ------------------

See #382
FindDCMTK - Clean white spaces
Merge branch '382-fix-find-dcmtk-issue' into 413-associated-dcmtk-definitions-to-ctkdicomcore

* 382-fix-find-dcmtk-issue:
  FindDCMTK - Clean white spaces
  FindDCMTK - Do not explicitly set DCMTK_DEFINITIONS

Conflicts:
	Utilities/CMake/FindDCMTK.cmake
Associate CTKDICOMCore with DCMTK_DEFINITIONS in build and install tree

Following commits a32f5242 and e984215, DCMTK_DEFINITIONS was associated
with the exported CTKDICOMCore target (install tree). At that time, it
was NOT required to associate  DCMTK_DEFINITIONS with CTKDICOMCore in the
build tree because FindDCMTK.cmake was calling "add_definitions(-D${DCMTK_DEFINITIONS})".

Then, as explained in commit b6b9bc220, the call to "add_definitions" has
been removed to prevent compile side effect in project building against CTK
and using the FindDCMTK.cmake provided by CTK.

This commit account for that change by explicitly associating the
DCMTK_DEFINITIONS with CTKDICOMCore target.

It also avoid redundant code used to set INTERFACE_COMPILE_DEFINITIONS by
moving the code from CTKGenerateCTKConfig to DICOM/Core/CMakeLists.txt

See #413
Merge branch '413-associated-dcmtk-definitions-to-ctkdicomcore'

* 413-associated-dcmtk-definitions-to-ctkdicomcore:
  Associate CTKDICOMCore with DCMTK_DEFINITIONS in build and install tree
  FindDCMTK - Clean white spaces
  FindDCMTK - Do not explicitly set DCMTK_DEFINITIONS