Feature request: copy selected images

[JingnaQiu]

• This is a function for the exact-test instance.
• The "copying images" function supports only imageset copy (i.e., all images will be copied). And if I just want to copy several images, I have to delete other images one by one.
• Extend this function by offering the opportunity of copying certain images from a certain imageset.
• Alternatively, make it possible to delete multiple selected images at once.