Merge branch 'feat/agipd-darks-speedup' of ssh://git.xfel.eu:10022/detectors/pycalibration into feat/agipd-darks-speedup

This commit does too many things, sorry, but stuff was all tangled up:
- clean up a bit (imports, unused variables)
- map to PDU with one query instead of in loop (each query gets all anyway)
- start fetching old constants (for comparison) in the background
- add qm layer to dict holding old constants (see issue #49)

This is kind of overkill (also throwing processes with threads at this
particular cell), but it does in my testing save something like half a minute.

This commit does too many things, sorry, but stuff was all tangled up:
- clean up a bit (imports, unused variables)
- map to PDU with one query instead of in loop (each query gets all anyway)
- start fetching old constants (for comparison) in the background
- add qm layer to dict holding old constants (see issue #49)

Add missing sphinx dependency to setup.py

See merge request detectors/pycalibration!473

[AGIPD][CORRECT] disable rel_gain with fixed gain and remove unused parameter

See merge request detectors/pycalibration!472

Make max_nodes a parameter for AGIPD correction notebook

See merge request detectors/pycalibration!467

Closes calibration_workshop#260

See merge request detectors/pycalibration!471

Add --slurm-partition CLI parameter to xfel-calibrate

See merge request detectors/pycalibration!469

fix key error modules_mappings

See merge request detectors/pycalibration!468