[Standards] New ProtoXEP: Jingle Content Category

Hi everyone, I'm submitting a new ProtoXEP named Jingle Content Category. The goal of this new XEP is pretty straightforward as described in its introduction: /This specification defines an XMPP extension to negociate the use of Session Description Protocol (SDP) media-level attribute 'content' as defined by RFC 4796 with Jingle RTP sessions/ This XEP is really useful for clients, like Movim, that are handling several streams, especially video ones, per user and wants to know how to deal with them in their UI and flows (prioritize the screen-sharing by putting it in full screen, always put the sign-language stream in the bottom right corner...). I'd also invites clients that are already implementing Jingle such as Gajim, Dino, Conversations, Libervia to tag their contents using this XEP ;) You can find my PR there: https://github.com/xsf/xeps/pull/1475 Regards, edhelas