Merge Box and SpaceBox into Box; reduce code duplication

src/Decomposition/CartDecomposition.hpp

src/Decomposition/Decomposition.hpp

src/Decomposition/Domain_icells_cart.hpp

src/Decomposition/cuda/Domain_icells_cart_unit_test.cu

src/Decomposition/cuda/decomposition_cuda_tests.cu

src/Decomposition/ie_ghost.hpp

src/Decomposition/ie_loc_ghost.hpp

src/Decomposition/nn_processor.hpp

src/Decomposition/tests/CartDecomposition_unit_test.cpp

src/Decomposition/tests/nn_processor_unit_test.hpp

src/Grid/grid_dist_id.hpp

src/Grid/grid_dist_id_comm.hpp

src/Grid/grid_dist_util.hpp

src/Grid/tests/grid_dist_id_unit_test.cpp

src/Vector/cuda/vector_dist_cuda_func_test.cu

src/Vector/tests/vector_dist_unit_test.cpp

src/test_isolation.hpp