Port vtmk module scripts to slicer 4.2

Deal with some small API changes:

category->categories
contributor->contributors
node.SetModifiedSinceRead->nothing
Fixes for slicer4.2 API changes

ModelDisplayNode.Get/SetPolyData -> Get/SetInputPolyData
slicer.app.mrmlApplicationLogic -> applicationLogic
layoutManger.threeDView(d) -> layoutManager.threeDWidget(d).threeDView()
ENH: Upgrade cmake infrastructure for 4.2 s4ext compatibility

Add a toplevel CMakeLists.txt so the structure matches other
extensions.

Don't generate the s4ext file directly, instead rely on the slicer
build system to do it based on the variables we set.
COMP: fix a link error on mac build

For unknown reasons, the Slicer-build link files included a
-F /Libraries/Frameworks command line flag, but this is not
being passed down to the extension, leading to a link error like
the one below.  Here I explicitly add the flag as a workaround
until the underlying issue is fixed.


Linking CXX shared library lib/Slicer-4.2/qt-loadable-modules/libqSlicerSlicerVmtk4Module.dylib
ld: framework not found QtSvg
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[8]: *** [lib/Slicer-4.2/qt-loadable-modules/libqSlicerSlicerVmtk4Module.dylib] Error 1
make[7]: *** [CMakeFiles/qSlicerSlicerVmtk4Module.dir/all] Error 2
make[6]: *** [all] Error 2
make[5]: *** [SlicerVmtk4/SlicerVmtk4-prefix/src/SlicerVmtk4-stamp/SlicerVmtk4-build] Error 2
make[4]: *** [SlicerVmtk4/CMakeFiles/SlicerVmtk4.dir/all] Error 2
make[3]: *** [all] Error 2
make[2]: *** [SlicerVmtk4-prefix/src/SlicerVmtk4-stamp/SlicerVmtk4-build] Error 2
make[1]: *** [CMakeFiles/SlicerVmtk4.dir/all] Error 2
make: *** [all] Error 2
COMP: move extension definition to top level of git checkout

This appears to be required in order for the Upload process
to correctly detect that the extension exists.
Merge pull request #1 from pieper/master

fixes for slicer4.2