* to NavierStokesNonIsothermalVtkOutputFields

* NavierStokesCommonIndices -> NavierStokesIndices

* description of equations still missing

If we don't do this, things stay in a deflected state before starting
the assembly of the next element and newton convergence is lost. This
only affects cases where grid-wide flux variables caching is enabled.

Feature/2p docu

See merge request !697