starting cnversion to pykat2 and 3 compatibility

pykat/SIfloat.py

pykat/colours.py

pykat/commands.py

pykat/components.py

pykat/detectors.py

pykat/exceptions.py

pykat/finesse.py

pykat/node_network.py

pykat/param.py

pykat/plotting.py

pykat/profiling.py

pykat/structs.py