Redesign mask editor so it shows already while editing what you will get (WYSIWYG)
This removes the necessity of ROI to implement the "show" button (the button was necessary to to see the masking effects).
In a further step the mask presenter (which uses ROI functionality) could be removed, which was the motivation for the refactoring/redesign in the context of "remove ROI" (see #73 (closed)).
The changes in pictures:
A) Mask editor in BornAgain1.18, editing mode:
B) Mask editor in BornAgain1.18, after pressing "show result":