add an adjustable intensity factor for XPS spectra

[superstar54]

As suggested by @PNOGillespie in this comment. fix #627

Now, the user can scale the calculated spectra and compare them with experimental data. Here is an example for the PA molecule, green color is the experimental data.

[codecov]

Codecov Report

Attention: Patch coverage is 7.14286% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 75.77%. Comparing base (ccc0f2f) to head (2f223cd).

Files	Patch %	Lines
src/aiidalab_qe/plugins/xps/result.py	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #642      +/-   ##
==========================================
- Coverage   75.85%   75.77%   -0.09%     
==========================================
  Files          60       60              
  Lines        4312     4317       +5     
==========================================
  Hits         3271     3271              
- Misses       1041     1046       +5     

Flag	Coverage Δ
python-3.10	75.77% <7.14%> (-0.09%)	⬇️
python-3.9	75.79% <7.14%> (-0.09%)	⬇️

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[PNOGillespie]

Hi @superstar54. Though I agree that this is a necessary feature, I think that the code should scale the intensity of the experimental data rather than the simulated data.

This is for the simple reason that, as the intensities of the computed spectra are modified whenever intensity is changed, the Result panel has to re-draw the entire plot from scratch. Scaling the intensity of the experimental data instead means that only one trace in the plot object needs to be updated, which is considerably faster.

I have a potential way to do this, but the changes are too extensive to easily show as suggested changes, so I will open a PR to your feature branch shortly.

[superstar54]

As discussed with @PNOGillespie , we think it's better to provide an initial scale value for the user.

[superstar54]

@PNOGillespie Now, the app will calculate an initial guess for the intensity factor, by aligning the max value of the total spectra with the max value of the experimental data. Please review.

[PNOGillespie]

Looks good to me! I think the last change particularly does a lot of good for usability. Good work @superstar54.