some foundational changes to migrate to noLegacyStyle

Please note that this PR will not change the currently published Editor's draft. It's going into a different branch (called `noLegacyStyle`). 

Note also the introduction of a "Telephony Services" section. The diagrams now moved into subsections that capture incoming and outgoing calls. Telephony eventing model now happens in those section instead of being defined per EventHandler attribute.