support generating flowed text for text/plain messages "Format=Flowed"
Support composing flowed lines as specified in RFC 3676 (supersedes RFC 2646). This will result in better user experience with word wrapping (newlines) and quoting in plain text messages (see #756 (closed)). See also problem description.
This issue supersedes Bug 200423 and is related to #248 (closed) and #403 (closed).