Fixes for Distortion of None

[psavery]

For LLNL, a distortion of None will most often be used. When the distortion is None, there shouldn't be parameters for the distortion function in the tree view. There will be a few things that need to be done.

• Remove the distortion function parameters from the default instrument config, so they don't get set automatically when a config file is loaded
• When the distortion is selected to be None via the form view (see below), remove the distortion parameters from the HexrdConfig instrument config, so they do not appear in the tree view
• When the distortion is changed from None to something else, add distortion parameters to the HexrdConfig instrument config

It appears that the form view already hides the parameters when None is chosen for the distortion function, which is correct. Now, we'd just need to get it to remove the parameters from the internal instrument config, and then add them back in if if the user switches to a different distortion other than None.

This function might be useful for this.

[cjh1]

Thanks