CamelIMAPXExtdStore: added own code paths for (extended) untagged response handler
CamelIMAPXExtdStore: added own code paths for (extended) untagged response handler

* added own code paths to override the ones leading
  to the execution of CamelIMAPXServer::imapx_untagged(),
  so that our own modified variant of the function
  will be called later on (the functions in CamelIMAPXExtdServer)
* added/changed implementations for connecting and
  authenticating to the IMAP server (since these all
  end in the untagged response handler)
  (this is still WIP, the code paths are not yet
  fully used)

GNOME/evolution-kolab,GNOME/evolution-kolab