new mesh from exo file

[echoi]

• A new mesh-importing function has been created to import a mesh in the ExodusII format, which is typically created with a meshing tool like Trelis.
• An 3D example input, examples/kenner_and_segall.cfg, is provided. The corresponding exodus mesh file and journal files to be used on Trelis are examples/exomesh.
  • The example runs up to 250 kyrs and performs remeshing once.
  • Geological relevance is weak but the example demonstrates the new capability of importing exodus meshes.