Import existing cameras for vrg gen

[amymmorton]

For larger scale testing of the wrist data- it would be very helpful to be able to load a previous set of cam calibrations as input for the vrg gen

[vforcesar]

Additionally, it would be helpful if the calibration and radiograph files updated automatically. Currently, I have to delete these files whenever I modify the cameras.

[jcfr]

very helpful to be able to load a previous set of cam calibrations

Currently the function onGenerateVRG (see below) ends up calling RadiographGeneration.generateNCameras() and IO.generateCameraCalibrationFile() (see below), to support this, we should skip the generation of the calibration files by allowing the user to select an existing directory with camN.json files.

The following UI needs to be updated implementing the following changes:

• Move # of Possible Cameras and Camera offset up
• Add radio buttons for toggling between automatic generation vs batch load of possible cameras

The following UI needs to be updated implementing the following changes:

• Add radio buttons for toggling between automatic generation vs batch load of possible cameras
• Add selector to pick existing directory containing optimized camera calibration files

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https://github.com/BrownBiomechanics/SlicerAutoscoperM/blob/7a2dd0fa87ad537a05745499b7c9c93c2491439d/AutoscoperM/AutoscoperM.py#L460-L469

https://github.com/BrownBiomechanics/SlicerAutoscoperM/blob/7a2dd0fa87ad537a05745499b7c9c93c2491439d/AutoscoperM/AutoscoperM.py#L542-L555