Added FFMpegPlugin (video thumbnails) and perception-based ImageSorter.
Added source code of sample plugins and additional plugins for specific cases.
Added plugin support for sorting.
Made NoThumbThreshold only affect metadata extraction (now generating thumbnails for files of any size).
Changed NoThumbThreshold default from 200 MiB to 20 MiB.
Now hiding Tags and other windows when main window goes to tray.
Added /hidden startup option.
Fixed various problems with system tray icon.