backup and restore of grid and dofvector

src/amdis/Mesh.hpp

src/amdis/PeriodicBC.inc.hpp

src/amdis/ProblemStat.hpp

src/amdis/ProblemStat.inc.hpp

src/amdis/common/FieldMatVec.hpp

src/amdis/common/FieldMatVec.inc.hpp

src/amdis/operations/FieldMatVec.hpp

test/BackupRestoreTest.cpp

test/CMakeLists.txt