Update the auto-stretch scheme and UI
Summary:
Modifies the auto-stretch algorithm.
Also, the UI is modified. When images are viewed, they can be viewed stretched or unstretched
and this can be toggled via a button in fitsviewer or on the floating tool bar in a fitsview.
This stretching does not modify the contents of the image.
Test Plan:
Open a variety of fits images in fitsviewer and from captures in the capture, focus, align and guide tabs.
See if they can be stretched and unstretched.
Reviewers: mutlaqja, wreissenberger
Reviewed By: mutlaqja, wreissenberger
Subscribers: lancaster, TallFurryMan, wreissenberger, kde-edu
Tags: KDE Edu
Differential Revision: https://phabricator.kde.org/D25318