imap: Made STATUS handling API more flexible.

imap: Mailbox names in STATUS replies were sent as UTF-8 instead of mUTF-7.

lib-storage: Moved some items from mailbox_get_status() to a new mailbox_get_metadata(). The idea is now that all status items are tracked all the time after mailbox is opened and they can always be looked up without failure. The metadata items are looked up lazily and the lookups may fail at any time. mailbox_get_status() can be used after mailbox_alloc() to indicate that the mailbox doesn't necessarily have to be opened, just that the status fields get returned. If mailbox is already known to be open, mailbox_get_open_status() can be used. It never fails.

lib-storage: STATUS_GUID moved to mailbox_get_guid() that can fail. --HG-- branch : HEAD

imap: Don't send NONEXISTENT resp code to non-delete operations. --HG-- branch : HEAD

Initial commit for making mail_storage:mailbox_list to be from 1:1 to n:n. This will allow namespaces to share the same storage and a single namespace to have multiple storages (multiple mailbox formats). Neither works currently, and this commit probably breaks some things. --HG-- branch : HEAD

Changed .h ifdef/defines to use <NAME>_H format. --HG-- branch : HEAD

Moved STATUS handling code to imap-status.[ch] --HG-- branch : HEAD