Added modular finite difference test code 'fd_catalog'.

kokkos-testing/CMakeLists.txt

kokkos-testing/experimental_data/timings.plot

kokkos-testing/fd_catalog/CMakeLists.txt

kokkos-testing/fd_catalog/fd_dataio.hpp

kokkos-testing/fd_catalog/fd_grid.hpp

kokkos-testing/fd_catalog/fd_main.cpp

kokkos-testing/fd_catalog/fd_wave.hpp

kokkos-testing/fd_catalog/fd_wave_cpu.hpp

kokkos-testing/fd_catalog/fd_wave_cuda.cu

kokkos-testing/fd_catalog/fd_wave_cuda.hpp

kokkos-testing/finite_difference_baseline.cpp

kokkos-testing/finite_differences.cu