Merge branch 'feature/scotch-matrix-reordering' into 'master'

Feature/scotch matrix reordering

Reordering the matrix leads to improved sparsity pattern. This is especially important for growing network grids.

Reordering results using the ReorderingDofMapper implemented by this MR with a growing network grid.

* Original unsorted FoamGrid
![original](/uploads/4f29ec169127ea67dbe814f6ee9daab5/original.png)
* Reordered dof indices
![reordered](/uploads/e2ade49c081353981b00cdf8ce7b2c51/reordered.png)


See merge request !186