backend, frontend: prepare remote control: This is a series of changes necessary to prepare the implementation of remote control feature: - XEP-0166: add a `priority` attribute to `ApplicationData`: this is needed when several applications are working in a same session, to know which one must be handled first. Will be used to make Remote Control have precedence over Call content. - XEP-0166: `_call_plugins` is now async and is not used with `DeferredList` anymore: the benefit to have methods called in parallels is very low, and it cause a lot of trouble as we can't predict order. Methods are now called sequentially so workflow can be predicted. - XEP-0167: fix `senders` XMPP attribute <=> SDP mapping - XEP-0234: preflight acceptance key is now `pre-accepted` instead of `file-accepted`, so the same key can be used with other jingle applications. - XEP-0167, XEP-0343: move some method to XEP-0167 - XEP-0353: use new `priority` feature to call preflight methods of applications according to it. - frontend (webrtc): refactor the sources/sink handling with a more flexible mechanism based on Pydantic models. It is now possible to have has many Data Channel as necessary, to have them in addition to A/V streams, to specify manually GStreamer sources and sinks, etc. - frontend (webrtc): rework of the pipeline to reduce latency. - frontend: new `portal_desktop` method. Screenshare portal handling has been moved there, and RemoteDesktop portal has been added. - frontend (webrtc): fix `extract_ufrag_pwd` method. rel 436

=========================================
ping: get response time of an XMPP entity
=========================================

``ping`` is more or less the equivalent of the command of the same name on most OSes, but
for XMPP. It send a `XEP-0199`_ PING and wait for the answer. When (and if) received, the
time to receive the answer is shown, else the time to receive the error message is shown.
This can be helpful to quickly test the connection with the server or a device.

If you need to get only the response time (without text around), you may use ``-d,
--delay-only``.

.. _XEP-0199: https://xmpp.org/extensions/xep-0199.html

example
-------

Get reponse time of a server::

  $ li ping example.org