Add channel transport with remeshing

[fsimonis]

This PR adds support for adaptive mesh refinement to the transport solver of the channel transport tutorial.

The transport-nutils runs normally without arguments.
Using ./run.sh remesh=True enables adaptive mesh refinement every 2 time windows. This mode starts with a mesh of a quarter of the total cells.
Using ./run.sh remesh=True frequency=5 sets the refinement frequency to every 5 time windows.

Checklist:

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[uekerman]

This is the case that we specifically set up as a testcase for remeshing. No need to copy in my opinion. Simply edit it directly.

#269

[fsimonis]

@uekerman This way, we lose our simple volume-coupling case though.

[uekerman]

There are enough other cases for volume coupling.

[fsimonis]

Merged the solvers, and updated OP

[MakisH]

Very nice test case! 👍

I ran it and the results look good: I see the updated mesh, and the simulation completes normally.

• The fluid-nutils/transport-nutils case took me 2h.
• The fluid-openfoam/transport-nutils case took me 20min.

Not sure if it makes sense to document somewhere that Nutils, especially the fluid-nutils, takes comparatively too long. Mainly to guide the user to prefer the faster OpenFOAM case and to not blame the runtime solely on preCICE.