Rendering Settings dialog is broken on Mac

[Peter Ellis]

Many of the controls in the Rendering Settings dialog are broken on Mac:

• The Variable Type radio button (Surface/Zone) doesn't update the label below it or the output variable drop-down lists.
• The Color Scheme drop-down menu doesn't update the color scale image.
• The Match variable range checkbox doesn't enable/disable the Minimum/Maximum fields.

The problem seems to be due to the fact that WebDialogs on Windows are synchronous while WebDialogs on Mac are asynchronous. The Rendering Setting dialog tries to send two different callbacks to window.location. Seems like only one gets through on Mac. The best solution is probably to update to the newer HTMLDialog class.