added licensing information (BSD-3) to source files

example/ALL_test.cpp

example/ALL_test_f.f90

include/ALL.hpp

include/ALL_CustomExceptions.hpp

include/ALL_Point.hpp

include/ALL_Staggered.hpp

include/ALL_Tensor.hpp

include/ALL_Unstructured.hpp

src/ALL.cpp

src/ALL_fortran.cpp

src/ALL_module.f90