Cleanup/simplify so subscribed option can be added
[mms] Added the MBOX_ALL_SUBSCRIBED mode to Horde_Imap_Client_Base#listMailboxes().

[mms] Fix broken MBOX_UNSUBSCRIBED behavior on IMAP servers that support LIST-EXTENDED.
[mms] Delimiter information is now always returned from Horde_Imap_Client_Base#listMailboxes().
Fix display of subscribed vs. unsubscribed mailboxes