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

-----BEGIN CERTIFICATE-----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==
-----END CERTIFICATE-----