Added license and license headers.

src/maxwell/maxwell_kernels_cuda.cu

src/maxwell/maxwell_postpro.cpp

src/maxwell/maxwell_solver.cpp

tests/profile_differentiation_gpu.cpp

tests/test_basics.cpp

tests/test_differentiation.cpp

tests/test_differentiation_gpu.cpp

tests/test_lifting.cpp

tests/test_lifting_gpu.cpp

tests/test_mass.cpp