ENH: Moved core module subject hierarchy plugins to related module

Subject hierarchy plugins project contained plugins for core modules
Markups, Models and Volumes. Those plugins are now in the
SubjectHierarchyPlugins subdirectory of those loadable modules.
Also the subject hierarchy support moved from
SlicerRT/DicomRtImport/DicomRtImportPlugin.py to
DICOMScalarVolumePlugin.py. Now the loaded DICOM scalar volumes are
automatically added to subject hierarchy.

From: Csaba Pinter <csaba.pinter@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23237 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Sank addSeriesInSubjectHierarchy function down to abstract DICOMPlugin

The addSeriesInSubjectHierarchy function (which was in DICOMScalarVolumePlugin so far) adds
the loaded node to subject hierarchy to the proper patient (subject) and study according to
the DICOM tags from the first file referenced in the associated loadable. This function is
now accessible from all the DICOM plugins. It needs to be called after the loaded object is
created in the load() function. Now it is called by DICOMDiffusionVolumePlugin too.

From: Csaba Pinter <csaba.pinter@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23238 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: vtkMRMLHierarchyNode methods made virtual

Two methods in vtkMRMLHierarchyNode made virtual. GetAssociatedChildrendNodes contained
a typo so it is now called GetAssociatedChildrenNodes. Subject hierarchy volumes plugin
now can add volumes from potential list to tree

From: Csaba Pinter <csaba.pinter@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23239 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: MRMLCLI_INCLUDE_DIRS CMake variable exported

It is needed for some subject hierarchy plugins to include the MRMLCLI indlude
directories, and by exporting this variable it is possible to do it without
manually constructing the paths in the CMakeLists files

From: Csaba Pinter <csaba.pinter@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23240 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Subject hierarchy python tests moved to SlicerApp

As the subject hierarchy tests cover multiple modules, they have been moved
from the SubjectHierarchy folder to Applications/SlicerApp/Testing/Python;
Occasional SlicerRT strings removed/replaced in subject hierarchy code
(mostly include dir comments)

From: Csaba Pinter <csaba.pinter@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23241 3bd1e089-480b-0410-8dfb-8563597acbee