Support RFC5258 & RFC5819 - LIST command extensions and STATUS information in Extended LIST

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These two RFC's deal with extended LIST operations to make them more efficient. We already see the problem with 1,200+ folders and the apple mail client that has to send a STATUS request for every mailbox. That is a lot of commands every minute, most of which return no new information. With IMAP clients that support the LIST command extensions they can get the same data back with the single LIST command. Definitely preferable and with our approach of now keeping all the mailbox meta information loaded in to memory it would also be no additional burden resource wise.