Extract attachment processing from forms, views.staff, and management.command.get_email modules, and consolidate it into a unified lib module function.
Also refactor the affected components, most notably lib.send_templated_email, to make it easier (IMO) to reason about changes to them.
Add unit tests for attachments with UTF-8 filenames, and functional tests for submission of same, as well as ASCII versions, through the public ticket-form.
Remove unused Attachment method "get_upload_to".
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