Refresh container listing after copying objects

[mgeisler]

When copying objects, it is possible that the current container listing shown behind the modal gets out of date: if copying foo.txt to nested/foo.txt in the same container, we should now show an entry with nested/.

We can either do this by trying to compute the new state (the same way we handle uploads and deletions) or we can reload the data when the modal is closed (easy).