https://github.com/assimp/assimp/issues/746
https://stackoverflow.com/questions/38296756/what-is-the-idiomatic-way-in-cmake-to-add-the-fpic-compiler-option

Unless option have to be passed using the command line, this is the
recommended approach to pass options. It avoids "command line length issues".

Adding of a step for the configuration of iMSTK with OpenHaptics

Contributor: Alexis Girault <alexis.girault@kitware.com>

Co-Authored-By: Alexis Girault <alexis.girault@kitware.com>

googletest git repository was using the SSH protocol
instead of HTTPS, which requires users to add an
ssh_key on github.com.

We switch all those external projects to HTTPS protocol,
but keep the ones hosted by ourselves on gitlab.kitware.com
in SSH since we might be contributing back to those
during development.

1) Only output to CMAKE_XXX_OUTPUT_DIRECTORY without
worrying about CMAKE_CONFIGURATION_TYPES

2) Use CMAKE_CFG_INTDIR to correctly set CMAKE_LIBRARY_PATH
after the change 1)

3) Use mark_as_superbuild() to pass variables to external
projects and innerbuild. (${PROJECT_NAME}_EP_ARGS)

4) Remove unecessary steps in eigen project (only includes, no lib)

5) Use standard imstkAddExternalProject for Uncrustify (not tested)

All projects output directories are now common in
the top level. This commit takes care of the
CMAKE_CONFIGURATION_TYPES for Visual Studio.

With this commit the Find_XXX.cmake files do not need
HINTS anymore since all targets are built in a same
directory known to CMAKE_LIBRARY_PATH, and all headers
directories are referenced in CMAKE_INCLUDE_PATH.