Changes to Distortion widgets in Instrument Calibration

[psavery]

We should add a "None" option to the "Function" combo box list, as sometimes there will be no distortion functions for the detector.

Also, different functions use different numbers of parameters. The GE_41RT uses 6 parameters, and a new one that will be added next week uses 8 parameters.

Perhaps we should remove the parameter widgets and put a "Configure" button, which pops up a dialog, and then the dialog will provide the edit-able widgets (and the correct number of them).

We could also just change the number of widgets in the instrument calibration panel depending on the currently selected distortion function.

Changes requested by @joelvbernier

[joelvbernier]

distortion can be a pop-out. we will move the distortion module to a package utilizing abstract base classes and a registry so we can add functions. The API for a distortion class will have a property yielding the number of parameters and their names...

[psavery]

I think this one can be closed in favor of #379. We will continue exploring new options for the distortion, though.