sub-optimal functionality in mail system

[mounty]

These are two suggestions to improve the way mail is handled.

1. Folders should show the extended attribute When, not the creation date of the mail item, which, in the case of a newly-discovered IMAP server, is utterly irrelevant. In a mail folder, you want to see the date of the email, not when the file was created by the mail_daemon.

2. An IMAP server with nested folders shows a flat dot-separated list of folders, rather than a hierachy. I know this reflects the raw structure, at least on a Dovecot database, but it's still not what I expect as a user. For example, I have a folder Incoming which contains one subfolder for each year: Incoming/2013, Incoming/2012 etc. In Haiku's folders, these are shown as Incoming.2013, Incoming.2012, all in one big list. What I would expect is just the folder Incoming, which, when clicked, opened a further folder window showing 2013, 2012 etc.