Move single dsp.py into ../rtdsp package with separate sub modules.

applications/lofar2/model/pfb_os/README.txt

applications/lofar2/model/pfb_os/filter_design_firls.ipynb

applications/lofar2/model/pfb_os/filter_design_remez.ipynb

...ons/lofar2/model/pfb_os/filter_design_windowed_sync.ipynb

...s/lofar2/model/pfb_os/hilbert_transform_application.ipynb

...ations/lofar2/model/pfb_os/hilbert_transform_design.ipynb

applications/lofar2/model/pfb_os/iir_filter.ipynb

...ions/lofar2/model/pfb_os/narrowband_noise_generator.ipynb

applications/lofar2/model/pfb_os/pfb_reconstruction.ipynb

...ofar2/model/pfb_os/rectangular_window_and_ideal_lpf.ipynb

...ions/lofar2/model/pfb_os/square_root_nyquist_filter.ipynb

applications/lofar2/model/pfb_os/up_down_sampling.ipynb

applications/lofar2/model/rtdsp/README.md

applications/lofar2/model/rtdsp/__init__.py

applications/lofar2/model/rtdsp/firfilter.py

applications/lofar2/model/rtdsp/fourier.py

applications/lofar2/model/rtdsp/hilbert.py

applications/lofar2/model/rtdsp/iirfilter.py

applications/lofar2/model/rtdsp/multirate.py

applications/lofar2/model/rtdsp/plotting.py