Merge branch 'issue/petsc_3-7' of https://gitlab.math.tu-dresden.de/iwr/amdis...

AMDiS/cmake/enable_hypre.cmake

AMDiS/cmake3/amdis_seq_petsc.cmake

AMDiS/cmake3/target_enable_hypre.cmake

AMDiS/src/ProblemStat.cc

AMDiS/src/parallel/PetscHelper.h

AMDiS/src/solver/BlockPreconditioner.h

AMDiS/src/solver/KrylovPreconditioner.h

AMDiS/src/solver/PetscSolver.h

AMDiS/src/utility/PetscWrapper.h

extensions/demo/pfc/CMakeLists.txt

extensions/demo/pfc/init/pfc.dat.2d

extensions/demo/pfc/init/pfc_rb.mtl.dat.2d

extensions/demo/pfc/init/pfc_solver.inc

extensions/demo/pfc/src/pfc.cc

extensions/demo/pfc/src/pfc_rb.cc

extensions/demo/pfc/src/vpfc.cc