Offline ETL virtualization and pacing

[planetchili]

For testing and validation we would like to play back ETL files through the service can consume them from test harness / overlay. A common virtualized interface is the cleanest solution, but currently PresentMonSession is not actually being dynamically bound.

• Re-architect the PresentMonSession interface for full dynamic binding (owner should mostly operate identically whether realtime or offline session is the underlying type)
• Review the PresentMon container class to improve interaction and control of PresentMonSession(s)
• Add the ability to control pacing of ETL (offline) events
• Implement pacing mode that paces to approximately the same cadence that they were captured at (for testing E2E to overlay)
• Implement pacing mode that paces to a fixed time step cadence with backpressure mechanism (for automated testing)
• Adjust timestamps of events, spoofing them to appear as realtime in the playback system or for consistency with automated test timeframes
• Add the ability to feed an ETL file to the service on the command line (unit test purposes)