The update of the reference solution was necessary as the problem description
did not fit the implementation. The current time in an implicit Euler context
has to be t+1.

The current implementation does not work with tensor permeabilities.
Not outputting the permeability as standard is suboptimal so we should
think about a better solution in the future.

* Remove permeability from the reference vtu files

* Implement problem interface functions mimicking the normal source interface
* Implement a possibility to implement derived point source classes getting cutomized lambda functions
	* the pointsource class gets an update method
        * An example implementation with test for time dependent point sources is implemented
* Restructure the point source class. Do not derive from PrimaryVariables (less felxible) instead overload
  some operators for convenience
* Call the solDependentPointSource function for each point source not per dof (multiple ps possible)
* Recompute the map for adapted grids