Uses QQuickImageProvider to return image for the imageviewer
Summary:
Refs T6268
uses QQuickImageProvider to display the images in imageviewer
Test Plan: the editings are broken now.
Reviewers: Koko, mart
Reviewed By: Koko, mart
Maniphest Tasks: T6268
Differential Revision: https://phabricator.kde.org/D7927