This is not done yet. Still have to fix a memory leak
that I don't quite understand yet + and some cleanups
and renamings are necessaryadds a new dialog that is shown when a file is closed (either when a new file is loaded or when Blender quits).
The memory leak is caused by some `IDP_CopyProperty`.
It looks like I call `IDP_FreeProperty` on my copy,
but obviously I'm missing something..."Save Images" checkbox does nothing at the moment.