[RCD] Feature suggestion: unsubscribe button

A feature that exists in Gmail that I'd like to see in Roundcube is an "Unsubscribe" button. This button can be used to unsubscribe from mailing lists automatically. It simply uses the "List-Unsubscribe" header which contains a link (usually a mailto) that the recipient can visit (or send an email to) to unsubscribe from the list.

The button would only show if this List-Unsubscribe header is present in the message being viewed. For an example, I've attached a screenshot of Gmail's unsubscribe button. It's to the right of the sender's email address.

If this is a welcome addition, I can try implementing it, but I haven't contributed to Roundcube before so I might not be able to get it right.