[ADD] filter_signal package, all others cleaned up and based on template

fft/CMakeLists.txt

fft/LICENSE

fft/README.md

fft/config/config.yaml

fft/fft/parameters.py

fft/fft/plotfourier.py

fft/include/cpp_python_package/cpp_publisher.hpp

fft/launch/fft.launch.py

fft/package.xml

fft/resource/fft

fft/setup.cfg

fft/setup.py

fft/src/cpp_publisher.cpp

fft/src/cpp_publisher_main.cpp

fft/test/test_copyright.py

fft/test/test_flake8.py

fft/test/test_pep257.py

filter_signal/config/.gitignore

filter_signal/config/cpp_publisher.yaml

filter_signal/config/filter.yaml