Deleting a collection deletes archived documents

[tommoor]

A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Archive a document
2. Delete collection
3. Archived documents are deleted

Expected behavior

It's probably more expected that archived documents hang around in the archive even if their original collection is deleted, as they don't appear in the sidebar it's otherwise easy to delete documents accidentally in this manner.