ISTL solvers and data structured usable

examples/ellipt.cc

examples/init/ellipt.dat.2d

examples/stokes0.cc

examples/stokes1.cc

examples/vecellipt.cc

src/amdis/Assembler.inc.hpp

src/amdis/LinearAlgebra.hpp

src/amdis/linear_algebra/DOFMatrixBase.hpp

src/amdis/linear_algebra/DOFVectorBase.hpp

src/amdis/linear_algebra/LinearSolver.hpp

src/amdis/linear_algebra/LinearSolverInterface.hpp

src/amdis/linear_algebra/istl/CMakeLists.txt

src/amdis/linear_algebra/istl/DOFMatrix.hpp

src/amdis/linear_algebra/istl/DOFVector.hpp

src/amdis/linear_algebra/istl/DirectRunner.hpp

src/amdis/linear_algebra/istl/Fwd.hpp

src/amdis/linear_algebra/istl/ISTLRunner.hpp

src/amdis/linear_algebra/istl/ISTL_Preconditioner.hpp

src/amdis/linear_algebra/istl/ISTL_Solver.hpp

src/amdis/linear_algebra/istl/LinearSolver.hpp