CamelIMAPXServer: Convert API to CamelIMAPXMailbox.

CamelIMAPXServer: Convert API to CamelIMAPXMailbox.

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()