Reverts back to using preview.png for thumbnails instead of mergedimage.png to...
requested to merge mourgos/krita:mourgos/Revert-back-to-using-preview.png-for-thumbnails into master
Reverts back to using preview.png for thumbnails instead of mergedimage.png to avoid excessive memory usage and processing time when dealing with high resolution images (bug report: https://bugs.kde.org/show_bug.cgi?id=431945).
This partially reverts behaviour introduced in: b8b657d2 This MR only affects the thumbnails shown in the docker. The page viewer changes for HiDPI support remain unchanged.