Dynamic plotter registration

Users shall be able to add, comment out or remove plotters at runtime without recompiling. The plotter ordering should not be fixed.

This is not too hard to obtain, just requires changes at KernelCalls.cpp with having a generated plotter registration function (semi pseudocode)

Writer* kernels::getNamedWriter(std::string name, Solver& solver) {
	if(name == "ConservedWriter") return new GRMHD::ConservedWriter(*static_cast<exahype::solvers::LimitingADERDGSolver*>(solver));
	if(name == "usw") return new GRMHD::SomeOtherWriter(*static_cast<exahype::solvers::ADERDGSolver*>(solver));
        if(name == ...
	else
		failure: Dont now this plotter type.
}

We then can replace the generated current section

  exahype::plotters::RegisteredPlotters.push_back( new exahype::plotters::Plotter(0,0,parser,new GRMHD::ConservedWriter(  *static_cast<exahype::solvers::LimitingADERDGSolver*>(exahype::solvers::RegisteredSolvers[0])) ));

  exahype::plotters::RegisteredPlotters.push_back( new exahype::plotters::Plotter(0,1,parser,new GRMHD::ConservedWriter(  *static_cast<exahype::solvers::LimitingADERDGSolver*>(exahype::solvers::RegisteredSolvers[0])) ));

  exahype::plotters::RegisteredPlotters.push_back( new exahype::plotters::Plotter(0,2,parser,new GRMHD::ConservedWriter(  *static_cast<exahype::solvers::LimitingADERDGSolver*>(exahype::solvers::RegisteredSolvers[0])) ));

  exahype::plotters::RegisteredPlotters.push_back( new exahype::plotters::Plotter(0,3,parser,new GRMHD::ConservedWriter(  *static_cast<exahype::solvers::LimitingADERDGSolver*>(exahype::solvers::RegisteredSolvers[0])) ));

  exahype::plotters::RegisteredPlotters.push_back( new exahype::plotters::Plotter(0,4,parser,new GRMHD::IntegralsWriter(  *static_cast<exahype::solvers::LimitingADERDGSolver*>(exahype::solvers::RegisteredSolvers[0])) ));

with a non-generated section (pseudocode)

for(const int& solvernum : Parser->getSolvers()) {
  int plotternum=0;
  for( const string& plottername : Parser->getPlotterNamesForSolver(solvernum)) {
      exahype::plotters::RegisteredPlotters.push_back(new exahype::plotters::Plotter(solvernum,plotternum++,parser,getNamedWriter(plottername, exahype::solvers::RegisteredSolvers[solvernum]));
  }
}

This is something I can do on my own. If the Parser gives the neccessary data...