[3p3c] adapt reference solutions

See merge request !848

Feature/make mpfafvgridgeom reusable

See merge request !839

[fluidsystems] fix evaluation of diffusion coefficients

See merge request !843

Differences to the release are sufficiently small.

Synchronizing the boundary condition evaluation points makes the
test pass. Keep the setting on the master, update the reference
solution, simplify the Neumann boundary condition.

Changes to the release are negligibly small.

[3p3c] update reference solutions

See merge request !845

Manually picked from 8aae0b9f.

Hard-coded values have been introduced accidentally in 704673b3.
Use the BinaryCoefficients instead.

[staggered][faceVariables] Retrive boundary values in fluxVars

See merge request !808

Feature/less typetag in vtkoutputfields

See merge request !840

* get the values for parallel and normal velocities directly in the
  fluxVars and not during the update of the faceVars
* this is necessary in the context of coupling when the velocities on the
  boundary shall be inferred from the other domain
* the gridFaceVars  are initialized (and thus updated)
  before any coupling context can be bound so this update step
  must not depend on some coupled context