CamelIMAPXStoreSummary has no public or private members, so no reason
to cast pointers to that type.  Stick with plain (CamelStoreSummary *).

Removed functions:

  camel_imapx_store_summary_new()

By default, Courier lists (("INBOX." ".")) for its personal namespaces,
which excludes INBOX itself.  This causes problems for us so check for
it specifically and hack around it where necessary.

No longer used.

Listing the mailbox will trigger our untagged LIST handler.  This
simulates being notified of a newly-created mailbox, so we can just
let the callback functions handle the bookkeeping.

Forget about namespaces when offline and just match folder paths.

Repurpose camel_imapx_server_list() to create/update CamelIMAPXMailbox
instances within CamelIMAPXServer.  This function no longer returns an
array of CamelIMAPXListResponses, but simply a success/failure boolean.

Also, this function no longer takes an extension string parameter.  If
the server names "LIST-EXTENDED" in its CAPABILITY response, then this
function automatically issues an extended LIST command:

    LIST "" $PATTERN RETURN (CHILDREN SUBSCRIBED)

Otherwise it issues a LIST command followed by an LSUB command:

    LIST "" $PATTERN
    LSUB "" $PATTERN

After camel_imapx_server_list() returns, the caller can then pass the
same $PATTERN string to camel_imapx_server_list_mailboxes() to obtain
an up-to-date list of CamelIMAPXMailbox instances that match $PATTERN.

Also as part of this, we now explicitly only list mailboxes in personal
namespaces.  Listing mailboxes in shared or other users namespaces is a
future enhancement since CamelStore does not yet have a suitable API to
support this properly.

Convert CamelIMAPXServer to primarily use CamelIMAPXMailbox instead of
CamelIMAPXFolder, the idea being to keep all the Camel-specific policy
and limitations relegated to CamelIMAPXStore and CamelIMAPXFolder, and
just have CamelIMAPXServer be a pure IMAP client implementation.

This is a huge commit which I don't like doing, but CamelIMAPXServer,
CamelIMAPXCommand and CamelIMAPXJob are so tightly intertwined that I
was unable to split this into smaller steps.

Added functions:

  camel_imapx_command_ref_mailbox()
  camel_imapx_job_has_mailbox()
  camel_imapx_job_ref_mailbox()
  camel_imapx_job_set_mailbox()
  camel_imapx_server_create_mailbox()
  camel_imapx_server_delete_mailbox()
  camel_imapx_server_rename_mailbox()
  camel_imapx_server_subscribe_mailbox()
  camel_imapx_server_unsubscribe_mailbox()

Removed functions:

  camel_imapx_job_has_folder()
  camel_imapx_job_ref_folder()
  camel_imapx_job_set_mailbox()
  camel_imapx_server_manage_subscription()
  camel_imapx_server_create_folder()
  camel_imapx_server_delete_folder()
  camel_imapx_server_rename_folder()

Modified function signatures:

  camel_imapx_command_new()
  camel_imapx_job_matches()
  camel_imapx_server_refresh_info()
  camel_imapx_server_sync_changes()
  camel_imapx_server_expunge()
  camel_imapx_server_fetch_messages()
  camel_imapx_server_noop()
  camel_imapx_server_get_message()
  camel_imapx_server_copy_message()
  camel_imapx_server_append_message()
  camel_imapx_server_sync_message()
  camel_imapx_server_manage_subscription()
  camel_imapx_server_update_quota_info()
  camel_imapx_server_uid_search()
  imapx_parse_status()

Processes a CamelIMAPXMailbox by adding relevant information to the
CamelIMAPXFolder, and invalidating the local cache if a UIDVALIDITY
change is detected.