Fix IMAPMessage::processFetchResponse bad_field_value_type for Cc and Bcc fields

IMAPMessage::processFetchResponse attempts to set Cc and Bcc header field values to values of type mailboxList. headerFieldFactory registers these fields with type addressList, resulting in bad_field_value_exception for IMAP messages containing a Cc or Bcc field.
Fixed by converting header field values for Cc and Bcc fields to addressList before setting header field values.