Add ZippedETL.cs to files to build for TraceEvent project
Add ZippedETL.cs to files to build for TraceEvent project

This fixes compilation errors in the samples about ZippedETLReader and ZippedETLWriter not being available when using the DLLs built for PerfView.

vancem/perfview,vancem/perfview,vancem/perfview,vancem/perfview,vancem/perfview