* Incremental fixes
* Fix base assignment of async delegate block reference
* Reuse existing memory blocks
* Remove PlaybackStarted child activity
The PlaybackStarted property is unnecessary, since the PlayAudio activity already completes right after playback has started.
* Add GetCallStatus API method
* Prevent variables on composite activities to be overwritten during deserialization
* Remove unnecessary variable declarations
Activity variables will be declared automatically during activity invocation.
* Add XML comments
* Remove unused references arg
* Streamline variable identity assignment
* Fix composite early exit completion
* Move identity assignment to workflow definition service
