[Development] Can we reduce the number of XDMF Files for meshes from three to two?

[sblauth]

It might be possible to only write two XDMF mesh files when converting and importing from Gmsh - one with the mesh and subdomain tags and one with boundary mesh and tags. This would make the usual mesh.xdmf file redundant and this could be replaced by the mesh_subdomains.xdmf. This should be tested, as this would save quite some disk space.

The changes are not breaking the API: One would have to check, whether a _subdomains file is present and use the old method then, otherwise use only the two meshes.

[sblauth]

At the moment, I would not suggest doing so as this may break other features.