cleanup, renaming variables

da/baseclasses/dasystem.py

da/baseclasses/obs.py

da/baseclasses/observationoperator.py

da/baseclasses/optimizer.py

da/baseclasses/platform.py

da/baseclasses/statevector.py

da/carbondioxide/dasystem.py

da/carbondioxide/obs.py

da/carbondioxide/obspack.py

da/carbondioxide/obspack_geocarbon.py

da/carbondioxide/statevector.py

da/co2gridded/dasystem.py

da/co2gridded/statevector.py

da/examples/das.py

da/examples/dasgridded.py

da/examples/dasjet.py

da/platform/capegrim.py

da/platform/huygens.py

da/platform/jet.py

da/platform/maunaloa.py