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.

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

Minor fixes, pushing straight to mastser as one is a breaking bug, symlinks
in src/xfel_calibrate point to the wrong directory causing it to not be
able to find notebooks. Caught by !464 tests

Fix/editable install cython build

See merge request detectors/pycalibration!461

[DARKS] Saving detector modules mapping in calibrationMetadata YAML file to use for summary modular notebook

See merge request detectors/pycalibration!463

Add tests question to MR template

See merge request detectors/pycalibration!462

Add a test for get_pdu and initialize_from_db

See merge request detectors/pycalibration!459

Add AGIPD Fixed Gain Mode

See merge request detectors/pycalibration!438

Add AGIPD Fixed Gain Correction

See merge request detectors/pycalibration!451

Add instructions on setting up GitLab SSH to README

See merge request detectors/pycalibration!455

Fix SQL parameter for query-rid action

See merge request detectors/pycalibration!460