Engineering Diffraction Interface doesn't recalculate Van Norm Focus if one with the correct name is already in the ADS

[andy-bridger]

Describe the bug
Bug found when changing the Custom Cal File implementation in Engineering Diffraction.
Currently, when you supply a Custom CalFile in Crop Calibration and then hit Calibrate the ADS is populated with files with the suffix _Custom.
When you then run focus, the Vanadium focussing checks to see if engggui_curves_Custom exists and if so, just loads it in, otherwise it calculates it.
This means if you run a calibration for a custom .cal file and focus it, then change your mind and rerun the calibration with a different custom .cal file, when you now focus again, it will use the original calibration.
This is also a problem (probably more so) for using the Crop to Spectra

Fortunately, for Custom CalFiles if there are different numbers of detector groups in the two custom files you get an error Error in execution of algorithm Divide: Number of histograms not identical., but if you happen to provide the same number of groups (like Crop To Spectra which always combines spectra into one group) you would likely not notice and it can make a big difference to the intensities:

To Reproduce
You can create some custom cal files using:

# import mantid algorithms, numpy and matplotlib
from mantid.simpleapi import *
import matplotlib.pyplot as plt
import numpy as np

group_ws1 = CreateGroupingWorkspace(InstrumentName='ENGINX', 
                        ComponentName='ENGIN-X', 
                        CustomGroupingString='100001-100100,101001-101100, 102001-102100')
group_ws2 = CreateGroupingWorkspace(InstrumentName='ENGINX', 
                        ComponentName='ENGIN-X', 
                        CustomGroupingString='100001-100100,101001-101100')
group_ws3 = CreateGroupingWorkspace(InstrumentName='ENGINX', 
                        ComponentName='ENGIN-X', 
                        CustomGroupingString='114001-114100,111001-111100, 112001-112100')

tmp_dir = r"C:/Users/kcd17618/Documents/MantidScripts/CustomCalBug"

SaveCalFile(rf"{tmp_dir}/example_cal_file.cal", GroupingWorkspace = "group_ws1", )                   
SaveCalFile(rf"{tmp_dir}/another_cal_file.cal", GroupingWorkspace = "group_ws2", )   
SaveCalFile(rf"{tmp_dir}/third_cal_file.cal", GroupingWorkspace = "group_ws3", )   

Custom Cal Files:

• Open Engineering Diffraction interface
• Click Create New Calibration
• Enter 305738
• Click Crop Calibration
• Set Region of Interest to Custom CalFile
• Set Custom CalFile to (rf"{tmp_dir}/example_cal_file.cal"
• Click Calibrate
• Go to Focus tab
• Set Sample Run to 305761
• Set Vanadium to 307521
• Click Focus
• Should get first image spectra
• Clear the ADS
• Go back to Calibrate tab
• Set Custom CalFile to (rf"{tmp_dir}/third_cal_file.cal"
• Click Calibrate
• Go to Focus tab
• Set Sample Run to 305761
• Set Vanadium to 307521
• Click Focus
• Without clearing ADS
• Go back to Calibrate tab
• Set Custom CalFile to (rf"{tmp_dir}/example_cal_file.cal"
• Click Calibrate
• Go to Focus tab
• Set Sample Run to 305761
• Set Vanadium to 307521
• Click Focus
• Should get second image spectra
• Without clearing ADS
• Go back to Calibrate tab
• Set Custom CalFile to (rf"{tmp_dir}/another_cal_file.cal"
• Click Calibrate
• Go to Focus tab
• Set Sample Run to 305761
• Set Vanadium to 307521
• Click Focus
• Should get error

Custom Crop To Spectra:

• Open Engineering Diffraction interface
• Click Create New Calibration
• Enter 305738
• Click Crop Calibration
• Set Region of Interest to Crop To Spectra
• Set Custom Spectra to 2-102
• Click Calibrate
• Go to Focus tab
• Set Sample Run to 305761
• Set Vanadium to 307521
• Click Focus
• Should get first image spectra
• Clear the ADS
• Go back to Calibrate tab
• Set Custom Spectra to 500-900
• Click Calibrate
• Go to Focus tab
• Set Sample Run to 305761
• Set Vanadium to 307521
• Click Focus
• Without clearing ADS
• Go back to Calibrate tab
• Set Custom Spectra back to 2-102
• Click Calibrate
• Go to Focus tab
• Set Sample Run to 305761
• Set Vanadium to 307521
• Click Focus
• Should get second image spectra

Expected behavior
Each time you run a calibration, you should expect to use that calibration for focussing, regardless of what junk is already in the ADS

Screenshots

Platform/Version (please complete the following information):

• OS: [e.g. Windows, RHEL 7, Ubuntu, macOS]
• OS Version:
• Mantid Version [e.g. 6.0.0]

Additional context