Node-local domain decomp

[MTCam]

This change set brings changes from @majosm's fork (majosm@a444cdd), which makes mesh partitioning a node-local affair. Each physical compute node gets the mesh data (read from gmsh or generated) and locally partitions and distributes the mesh partitions among the ranks local to the physical compute node.

Questions for the review:

• Is the scope and purpose of the PR clear?
  • The PR should have a description.
  • The PR should have a guide if needed (e.g., an ordering).
• Is every top-level method and class documented? Are things that should be documented actually so?
• Is the interface understandable? (I.e. can someone figure out what stuff does?) Is it well-defined?
• Does the implementation do what the docstring claims?
• Is everything that is implemented covered by tests?
• Do you see any immediate risks or performance disadvantages with the design? Example: what do interface normals attach to?

[majosm]

I took a quick look through the code to see if the node-local code is up to date. Looks like it is, apart from one comment. This version also has the correct indentation for part_id_to_tag_to_elements.