Entity capabilities and mixer/call presence

[crienzo]

Issue #48 added entity capabilities to rayo presence events so that mixers and calls can be identified as such.

The rayo spec says to use the node to identify the entity as either a mixer or call, however XEP-0115 says the node is supposed to identify the software application, preferably a URI. Furthermore, a disco is to be performed to actually determine the capabilities of the entity.

I'm not sure why this is needed for calls. The fact that only calls send offer and the offer is in the rayo namespace should be enough to figure out the presence is from a call. Maybe the dial case was more problematic?

Similarly, with mixers, you see a mixer-name in the joined event which tells you that the presence is from a mixer.

[benlangfeld]

The problem is that mixer's URIs are indistinguishable from call's URIs, and they may both send identical events (eg output complete). We need some way to identify if the entity is a call or a mixer.