Structure for Examples Seciton

The SDP is all wrong in this but here is the structure I am proposing for the Examples section. This does not remove the appendix but I'd propose we remove the whole appendix if we add this. Let me know if this looks reasonable as the outline and if so we can sort out the details of the flows and fix the SDP. The current flows and SDP are based off the XMPP flow in the appendix. 
In this complex example, I think it would be valuable to also show a renegotiation, i.e. adding screenshare by the callee.