* On Windows and MacOS, no idea how themes work so only allow Linux to use their theme icons
* Internal icons are used by default on non-Linux platforms
* Also limit viewing features such as zoom levels when files have different dimensions
* GraphicsViewImageViewer is still a bit buggy: the scrollbars are toggled on when the pixmap is null in the reference viewer (we do not use that class right anyway)
* Use custom icons on platforms which do not provide theme
* Old zoom icons credits to "schollidesign" from icon pack Office and Entertainment (GPL licence).
* Exchange icon credit to Jason Cho (Unknown license).
* Use hack to resize viewers on first show() as well
* Add splitter in order to hide the details table.
* Add a toolbar to the Details Dialog window to allow for better image
comparisons: zoom in/out, swap pixmaps in place, best-fit-to-viewport.
Scrollbars and viewports are synchronized.
