Hand Gauss point index to helper functions of generic kernels

Rationale

This will enable us to implement the point source like solution adjustements required by the seismology people.

Proposed signatures

• static void eigenvalues(double* const x,int* const ix,double t,int it,double* const Q,int normalNonZeroIndex,double* lambda);
• static void flux(double* const x,int* const ix,double t,int it,double* const Q,double** F);
• static void source(double* const x,int* const ix,double t,int it,double* const Q,double* S);
• static void boundaryValues(double* const x,double* const ix,double t,int it,const int faceIndex,int normalNonZero,double * const fluxIn,double* const stateIn,double *fluxOut, double* stateOut);
• static void adjustedSolutionValues(double* const x,int* const ix,double t,int it,double* Q); ``

ix is the spatial Gauss point index (multiindex of size DIMENSIONS). it is the temporal Gauss point index.

Boundary values

We decided to sample pointwise and perform a time integration afterwards (global time stepping) or directly add the face's flux contribution to the cell's update.