Add XML support to the Custom CalFile in Engineering Diffraction Analysis

[andy-bridger]

Describe the issue
At the moment, if you want to group detectors you can use the presets or provide the path for a custom cal file with the suffix .cal. If you want to make and use your own grouping file, however, SaveDetectorGrouping outputs an xml file. It would be good if these could be used directly within the Crop Calibration interface

Describe the solution you'd like
Crop Calibration to support loading XML grouping files

Describe alternatives you've considered
None, currently just stuck using the presets

Additional context