Merged FiniteDifference and Sussman redistancing files from develop.

src/FiniteDifference/FD_order1.hpp

src/FiniteDifference/Upwind_gradient.hpp

src/FiniteDifference/tests/Eno_Weno_unit_test.cpp

src/FiniteDifference/tests/FD_order1_unit_test.cpp

src/FiniteDifference/tests/Gaussian.hpp

src/FiniteDifference/tests/Upwind_gradient_unit_test.cpp

src/level_set/redistancing_Sussman/HelpFunctionsForGrid.hpp

src/level_set/redistancing_Sussman/NarrowBand.hpp

src/level_set/redistancing_Sussman/RedistancingSussman.hpp

src/level_set/redistancing_Sussman/tests/TestHelpers.hpp

...distancing_Sussman/tests/analytical_SDF/AnalyticalSDF.hpp

...level_set/redistancing_Sussman/tests/convergence_test.cpp

src/level_set/redistancing_Sussman/tests/l_norms/LNorms.hpp

...l_set/redistancing_Sussman/tests/narrowBand_unit_test.cpp

...istancing_Sussman/tests/redistancingSussman_unit_test.cpp