Merge branch 'MC/multigpu' into devel

CMakeLists.txt

include/common/gpu_support.hpp

include/common/mpi_helpers.h

include/libgmshdg/gmsh_io.h

include/maxwell/maxwell_interface.h

share/examples/parallel_plate/params_parallel_plate.lua

src/libgmshdg/entity.cpp

src/libgmshdg/gmsh_io.cpp

src/libgmshdg/param_loader.cpp

src/libgmshdg/physical_element.cpp

src/libgmshdg/reference_element.cpp

src/maxwell/maxwell_gpu.cpp

src/maxwell/maxwell_interface.cpp

src/maxwell/maxwell_kernels_cuda.cu

src/maxwell/maxwell_solver.cpp