Convert HSL tool to new slider/text custom control
fix Median filter to work at a cutoff of 1
Convert Median tool to new slider/text custom control
Convert monochrome -> grayscale tool to new slider/text custom control
Convert Modern Art tool to new slider/text custom control
Convert Lens Correct tool to new slider/text custom control
Convert Lens Distort tool to new slider/text custom control
Convert Kaleidoscope tool to new slider/text custom control
Redesign (e.g. "greatly improve") Image Levels tool

Finally, after many years of waiting, I have redesigned the Image Levels
tool to something resembling every other tool in the project.  Input can
now be made via text boxes as well, for precise and accurate results.
The midtone slider has been converted from RGB range (0-255) to the more
sensible (0.0,1.0) range.  This allows the midtone ratio to stay
constant even while the black point and white point values are changed.

I had to change almost all text on the form, so additional translations
will be needed for the next release.