[test] Use new property for vtkOutput module in two tests

See merge request !391

* Test wouldn't compile

Feature/improve staggered local jacobian

See merge request !388

[implicit][problem] change positions of boundary and source evaluations

See merge request !385

[next] Clear local data before updating objects when grid changed

See merge request !389

* Build pressure difference with lower absolute values
* To prevent domination of pressure term in half-residuals

* Each derivative calculation can now be set with a specific base epsilon

[staggered][model] Slight modifications of staggered model

See merge request !386

Cleanup/staggered

See merge request !383

* faceIndices start at numCellCenterEquations ( > 0)
* Accessing a Dune::FieldVector<int,1> with an index > 0 does not yield any
  error, warning, segfault etc.

* Changed probably due to correction of volume term for face

* Use correct faceVars

* To supress compiler warnings

* Convert matrix (if required) in newtoncontroller, as done in
  mixeddimension

* Do not use fixed values anymore

Improve Richards model - Add RichardsNC model

See merge request !360

[test][richardsnc] Add mass-conservation-output. Use heavy water tracer. Flow rate in kg/s instead of mol/s