ENH: Add LibNiFalcon as external project

Needed for VRPN. Use fork made for cmake improvements
and plan for a pull request:
https://github.com/agirault/libnifalcon/tree/improve-cmake

CMake/External/External_LibNiFalcon.cmake

+#-----------------------------------------------------------------------------
+# Add External Project
+#-----------------------------------------------------------------------------
+include(imstkAddExternalProject)
+imstk_add_external_project( LibNiFalcon
+  GIT_REPOSITORY https://github.com/agirault/libnifalcon
+  GIT_TAG improve-cmake
+  INSTALL_COMMAND ${SKIP_STEP_COMMAND}
+  CMAKE_ARGS
+    -DBUILD_TESTING:BOOL=OFF
+    -DBUILD_EXAMPLES:BOOL=OFF
+    -DBUILD_SWIG_BINDINGS:BOOL=OFF
+    -DBUILD_SHARED:BOOL=OFF
+  DEPENDENCIES ""
+  RELATIVE_INCLUDE_PATH "include"
+  #VERBOSE
+  )

CMake/External/External_VRPN.cmake

@@ -3,7 +3,7 @@
 #-----------------------------------------------------------------------------
 set(VRPN_DEPENDENCIES "")
 if(WIN32)
-  list(APPEND VRPN_DEPENDENCIES Libusb) # "LibNiFalcon"
+  list(APPEND VRPN_DEPENDENCIES Libusb LibNiFalcon)
 endif(WIN32)
 
 include(imstkAddExternalProject)
@@ -23,7 +23,7 @@ imstk_add_external_project( VRPN
     -DVRPN_USE_GPM_MOUSE:BOOL=OFF
     -DVRPN_USE_LIBUSB_1_0:BOOL=ON
     -DVRPN_USE_HID:BOOL=ON
-    #-DVRPN_USE_LIBNIFALCON:BOOL=ON
+    -DVRPN_USE_LIBNIFALCON:BOOL=ON
   DEPENDENCIES ${VRPN_DEPENDENCIES}
   RELATIVE_INCLUDE_PATH ""
   #VERBOSE

CMakeLists.txt

@@ -92,7 +92,7 @@ imstk_define_dependency(Eigen)
 imstk_define_dependency(VegaFEM)
 imstk_define_dependency(VTK)
 imstk_define_dependency(VRPN)
-#imstk_define_dependency(LibNiFalcon)
+imstk_define_dependency(LibNiFalcon)
 
 #-----------------------------------------------------------------------------
 # SUPERBUILD