v1.5.7

• add preference for dark/light appearance (overriding system setting if desired)
• set text color of filenames to white against dark backgrounds
• fix heic auto-orientation in slideshow
• generate larger thumbnails in some cases when preference is set to 160
• remember rotations in between slideshows
• fix: app should no longer prevent unmounting of volumes
• fix animated gifs when "show large images at actual size" pref was on
• update slideshow image correctly when performing lossless jpeg rotation and "don't change modification date" preference was on
• fix order of slideshow when files were changed in the background and images were sorted by modification date
• eliminate white edges to images in certain circumstances
• fix a small memory leak when viewing exif info