nemo: copying files within the same file system should hardlink instead.

[HT-7]

Hardlinking is instant and saves space. Hardlinks behave just like copies. No apparent downsides on file systems which support it (ext4, XFS, NTFS, UDF), but only files can be hardlinked, not folders. If hardlinking fails for whichever reason, it should fall back to normal copying.

[HT-7]

Thinking about it, I realize it might not be a good idea because the user might want to edit files independently from each other. Self-closing.