Allow users to define name prefex of .zip attachment in Quickmail

The default naming scheme for .zip attachments in Quickmail is inflexible. In order to differentiate multiple .zip files coming from quickmail messages, the renaming process is determined only by the recipient (if they are savvy enough to rename the file when saving the attachment). A straight download of the file will result in OS-determined naming schemes similar to [archive.zip, archive-1.zip, archive-2.zip] which creates a directory of nondescript files difficult to identify their origin and content in a file browser.

Giving users cognisant of this default workflow the ability to customize the name of the resulting .zip file would help distinguish the content from other messages both within a single course and from other courses.