Merge branch 'feature/adaptive_grid' into 'master'

.gitlab-ci.yml

src/amdis/AdaptiveGrid.hpp

src/amdis/DOFVector.hpp

src/amdis/MeshCreator.hpp

src/amdis/Observer.hpp

src/amdis/ProblemStat.hpp

src/amdis/ProblemStat.inc.hpp

src/amdis/ProblemStatTraits.hpp

src/amdis/common/CMakeLists.txt

src/amdis/common/DefaultGridView.hpp

src/amdis/functions/ParallelGlobalBasis.hpp

src/amdis/io/FileWriterCreator.hpp

src/amdis/linearalgebra/petsc/MatrixNnzStructure.inc.hpp

test/AdaptiveGridTest.cpp

test/CMakeLists.txt

test/DOFVectorTest.cpp

test/GradientTest.cpp

test/ISTLCommTest.cpp

test/MarkerTest.cpp

test/ProblemStatTest.cpp