Room Activity Indicators

Issue related to the implementation of the activity of MUCs in converse

https://xmpp.org/extensions/inbox/room-activity-indicators.html

Summary:

• JC implemented a feature in converse to subscribe to RAI
• I have implemented a similar behavior in our current chat component
• We fixed with @MattJ some issues related to its implementation in server/client (wrong marker etc...)

Known issues:

• We still receive RAI from some messages that does not contain a body (e.g reactions)