Address most of modernize-use-auto

src/blockforest/BlockForest.cpp

src/blockforest/BlockID.h

src/blockforest/PhantomBlockForest.cpp

src/blockforest/StructuredBlockForest.h

src/blockforest/communication/UniformBufferedScheme.h

src/blockforest/loadbalancing/DynamicDiffusive.h

.../loadbalancing/weight_assignment/MetisAssignmentFunctor.h

src/core/Set.h

src/core/config/Config.h

src/core/debug/CheckFunctions.impl.h

src/core/mpi/SendBuffer.h

src/core/uid/UID.h

src/domain_decomposition/IBlock.h

src/field/Field.impl.h

src/field/FlagField.impl.h

src/field/GhostLayerField.impl.h

src/field/allocation/FieldAllocator.h

src/field/blockforest/BlockDataHandling.h

src/field/communication/PackInfo.h

src/field/iterators/IteratorMacros.h