* Update Boost external project to expect the library to be installed on
  the system.

* Add "SlicerSMTK" dependencies
  - aeva-session

* Add additional "smtk" dependencies:
  - MOAB
  - LibArchive
  - nlohmann_json (Copied from https://github.com/Slicer/SlicerJupyter)
  - pegtl
  - VTK
  - vtkIOParallelExodus

* Add CMake module for downloading VTKExternalModule project at configuration
  time. The module is used to build the "vtkIOParallelExodus" VTK module
  externally when SlicerSMTK is built as a standalone extension.

* Update CMake variable listing dependencies from "${proj}_DEPENDENCIES"
  to "${proj}_DEPENDS". The variable name is now consistent with convention
  used in Slicer extension SuperBuild template.

* Update build-system to support bundling the extension is a custom
  application.

* Update smtk to attempt to find externally built version of
  IOParallelExodus VTK modules

List of SMTK changes:

$ git shortlog fd9a4f17f..e1aef4180
Jean-Christophe Fillion-Robin (2):
      COMP: Attempt to find externally built version of IOParallelExodus VTK modules
      COMP: Update VersionNumber.cxx to support building against C++11