Port the save-saving patch from 3.1

BUG:370193 Save a copy of the image not the original

This restores the delayed saving dialog, which is now even weirder,
with a cancel running operating button which mostly doesn't work,
a do not save button, and a don't care, save a broken copy button.

See also

https://phabricator.kde.org/D3258
https://phabricator.kde.org/T4220
https://bugs.kde.org/show_bug.cgi?id=370566
https://bugs.kde.org/show_bug.cgi?id=369368
https://bugs.kde.org/show_bug.cgi?id=370193