L2SS-891: Refactor of DTS code

lofar_station_client/RCUs.py

lofar_station_client/dts/__init__.py

lofar_station_client/dts/bands.py

lofar_station_client/dts/common.py

lofar_station_client/dts/constants.py

lofar_station_client/dts/index.py

lofar_station_client/dts/outside.py

lofar_station_client/dts/plot.py

lofar_station_client/processing_lib.py

requirements.txt

tests/dts/__init__.py

tests/dts/test_bands.py

tests/dts/test_index.py