[Standards] XEP-0503: Spaces update proposal

Hi all, I just submitted a revision to XEP-0503: Spaces. This is something edhelas and I have been working on last week. I intend to implement it in slidge, and he intends to implement UI for it in movim. It is an almost complete rewrite vs the current state, which should not be an issue since it has not been implemented anywhere yet. I tried to incorporate the feedback I got, not only from the mailing but in various MUCs and private conversations I had about the XEP here and there. In short, a space is now just a pubsub node with appropriate configuration and payload, and a space service is a pubsub service with feature requirements. As per the previous revision, the goal of this XEP is to establish a minimal viable protocol for clients and servers to build around the general concept of grouping several entities together. It requires little to no additional support server-side and should work, in a very basic form, with what's already available out there. I believe, that, even in this basic form, it would be nice to have. edhelas and I will also submit soon(ish) another XEP which could be _a_ way of defining how space-wide affiilations/roles/hats could work, by using a "space's main MUC". That would allow for both optimising presence traffic and enforcing consistency between the various rooms of a space. This, of course, would require some additional server and client support, but it looks like we can do something that is relatively usable on any MUC-supporting client. I think it is best to have this in a separate XEP, for future-proofness, since GC3 is just around the corner. ;o) Let me know what you think. -- nicoco