Feature request: Copy/duplicate without packing

[squiddingme]

Seems like when a layer is duplicated or copied and pasted it always makes copies of all of the textures and packs those copies into the file. I'm not sure if there's a technical reason why this is the case but it causes projects to quickly balloon in file size.

I think the current copy/duplicate layer functions should make texture copies that aren't packed (they point to the same source as the original), and an extra set of functions "Duplicate Layer and Pack Textures" and "Paste Layer(s) and Pack Textures" could exist.

Either that or a toggle box in Ucupaint settings could switch between packing and unpacking behavior.