(cherry picked from commit 4f8d968c)

(cherry picked from commit 32d23008)

(cherry picked from commit 8d90cc94)

This was simply wrong. However NestedVtkFunction currently doesn't compile
if the mapper is a singlegeomtype mapper as it doesn't allow mapping elements
due to a static_assert.

This reverts commit e7e9c71d.

Feature/3p3c on next

See merge request !508

[staggered][localJacobian] Allow inherting classes access to faceVars

See merge request !545

* Specialization of the localJacobian need access to the non-const
  version of the faceVars. This concept might be revised.

Feature/simplify porousmedium fluxvars

See merge request !544

Should be part of a future PMFlow TypeTag

[fix] add update of subproblemsolution to newtonendstep

See merge request !543

Fix/make testscript compatible for python3

See merge request !538

Fix deprecation warning for Dune MCMG Mapper

See merge request !539

Fix/staggered use num boundary faces from global fv geometry

See merge request !541

* does not make sense for grids with holes in them