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

[
    {
        "main-language": "en",
        "name": "Libervia",
        "title": "Libervia",
        "short-desc": "Forums about Libervia demo",
        "sub-forums": [
            {
                "uri": "",
                "title": "tools and features",
                "short-desc": "Discussions about Libervia frontends, tools, features, or changes"
            },
            {
                "uri": "",
                "title": "questions and help",
                "short-desc": "Mutual assistance for installation or using Libervia and its ecosystem"
            }
        ],
        "desc": "Those are example forums."
    },
    {
        "main-language": "en",
        "title": "XMPP and associated",
        "sub-forums": [
            {
                "uri": "",
                "title": "XMPP software",
                "short-desc": "Topics about XMPP software other than Libervia"
            },
            {
                "uri": "",
                "title": "outside XMPP",
                "short-desc": "You can discuss or present here protocols or software similar to XMPP"
            }
        ],
        "desc": "Forums about XMPP in general, or similar protocols"
    }
]