Slack-like chat (also for GSOC)

[Chris Jones]

> I would say we can try Riot (also mentioned earlier by Rainer), as I
> see lot of pros put up for it in [1]. We can also explore discord as
> an option. If none works, we can stick to IRC.

I've been trying Riot out for a bit now, since this discussion started. 
Its not bad I would say..

( The main problem I have, is not something specific to Riot or whatever 
forum we use, but more we need to perhaps give some thought to the 
channels. Currently there is really only one, which gets (some) chat but 
also messages for each and every commit. I don't think the average user 
needs to see each and every commit. I think we probably need to split 
these, for instance into Dev and User channels, to match the mailing 
lists perhaps. )

Chris