Eigen solvers cleaned up

src/amdis/LinearAlgebra.hpp

src/amdis/LinearSolvers.hpp

src/amdis/ProblemStat.cpp

src/amdis/ProblemStat.hpp

src/amdis/QuadratureFactory.hpp

src/amdis/linear_algebra/DOFMatrixBase.hpp

src/amdis/linear_algebra/RunnerInterface.hpp

src/amdis/linear_algebra/eigen/DOFMatrix.hpp

src/amdis/linear_algebra/eigen/DirectRunner.hpp

src/amdis/linear_algebra/eigen/IterativeRunner.hpp

src/amdis/linear_algebra/eigen/PreconConfig.hpp

src/amdis/linear_algebra/eigen/SolverConfig.hpp

src/amdis/linear_algebra/eigen/SolverCreator.hpp

src/amdis/linear_algebra/istl/DOFMatrix.hpp

src/amdis/linear_algebra/mtl/DOFMatrix.hpp

src/amdis/utility/MultiIndex.hpp