This patch adds the ability to refine a editing mask by a color-range
based on the pixels of the content image. This is useful for image
editing where mask restirction via luminosity might not fit or just
certain color ranges should be edited.
This adds a function where editing masks can be refined by selecting
a luminosity range that is applied to the content image and mapped to
the editing mask. This function allows the editing of image regions
that match only certain luminosity values.
