If the boundary mesh is larger then the definition region
of the bulk component, then a nop is returned.
This usually indicates wrong geometry or something horrible.

Clang format run on near-the-header lines.

Happy New Year

This has some follow-up changes.

Don't repeat typename in emplace_back.

MSS---the mesh subsets.

MSS are the MeshSubsets.

This is just updating the interfaces and some of the for-loops
but will not compile until the using part is also updated.