Range handles in the Color opacity editor
Range handles are now shown in the color opacity editor widget They allow to very easily manipulate the range of the transfer function. By grabbing, moving and releasing a range handle, the range is interactively modified. The range is shown in the widget while interacting with the handles.
This also uses the add point item of the control point item, in order ot be able to grab the range handles as well as the control points.
This also correct a small update bug of the control point table.
Edited by Mathieu Westphal (Kitware)