issue #29: Config option for courier-imap servers.

courier-imap can be sent a FETCH with (SUBJECT TO FROM) and reply with ("SUBJECT" "TO" "FROM"). Sending the non-quoted version therefore doesn't work with Mail::IMAPClient because it will erase any entry that wasn't requested, see: https://metacpan.org/source/PLOBBES/Mail-IMAPClient-3.34/lib/Mail/IMAPClient.pm#L2286

I'm not sure if this is the actual RFC, or if dovecot works with quotes. This adds a config option to turn the quotes on in Model/IMAPClient.pm but if it works with dovecot I guess it doesn't need to be configurable.