[GridViewOrdering] Bugfix: Make sure block counts are calculated correctly on successive updates

We forgot to zero the relevant vector, only resizing it instead...
[stokesparameter] Add and fix Doxygen comments, remove superfluous semicolons.
Fix headercheck for variable*fem.hh.

Obvious typo.
Removed unused includes and superfluous semicolons.
Removed unused variables, typedefs and an included  header.
Merge branch 'feature/fixes-by-christoph'

Several fixes that were mixed in with the move of the constraints headers,
separated out for better readability.

Thanks to Christoph for these.

* feature/fixes-by-christoph:
  Removed unused variables, typedefs and an included  header.
  Removed unused includes and superfluous semicolons.
  Fix headercheck for variable*fem.hh.
  [stokesparameter] Add and fix Doxygen comments, remove superfluous semicolons.
Merge branch 'feature/move-constraints-headers'

Kudos to Christoph for doing all the tedious work!

I separately cherry-picked some commits into a separate merge because
they fix unrelated problems.

* feature/move-constraints-headers:
  Adapt benchmark problems to follow new location of constraints.
  [Constraints] Drop "constraints" in file name of constraints implementations.
  Remove old (pre-PDELab 2.0) transition header gridfunctionspace/constraints.hh
  [constraints] Reorganize location of constraints.
Add forgotten transition header for interiornodeconstraints.hh.