option: readflag_time_enable

[crpb]

Hi,

i would really like to configure a default(true/false) for readflag_time_enable because many people don't want it and it's easier to mark a mail as read than not realizing that you accidentally 'read' mails and turn it back.
And some people who use shared mailboxes just don't think about why it would be better 👀

~cb