issue: .eml/.msg Attachments

This addresses an issue where `.eml` and `.msg` files on incoming mails are
being dropped. This is due the the mail fetcher that tries to process
`.eml`/`.msg` files and adds them as thread entries rather than adding them
as attachments. This adds a new section that utilizes a new method to fetch
the body of `.eml`/`.msg` files, fetches the subjects of the `.eml`/`.msg`
files as the attachment names, and creates attachments. This preserves the
`.eml` and `.msg` files and adds them to the pertinent thread entries as
attachments.