Reorganized fd_catalog a bit.

kokkos-testing/experimental_data/timings.plot

kokkos-testing/experimental_data/timings2.txt

kokkos-testing/fd_catalog/CMakeLists.txt

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/finite_difference_kokkos.cpp

kokkos-testing/test_gemv.cpp

kokkos-testing/test_mandel.cpp

kokkos-testing/test_sumbw.cpp