Delete trashed documents permanently before 30 days

I've implemented permanent deletion of trashed documents. It works as you would expect; trashed documents receive an extra menu option called "Delete permanently", which reuses code from [api/utils.gc]( to destroy the document and its attachments.

![CleanShot 2020-12-24 at 16 38 21](

If you guys want it, I'll submit a PR with the changes.