added audio and video codec names in telemetry report

now telemetry report has two new parameters, audioName and videoName. Both are arrays to save the AV codec name used in each call.
I think it should be better
Replace line 152 to 168 with:

        if (!report) {
          report = new TelemetryReport();
        } else {
          if (report[type] === undefined) {
            var newReport = new TelemetryReport();
            // Copy the new fields..
            for(var key in newReport) {
              if (report[key] === undefined) {
                report[key] = newReport[key];
              }
            }
          }
        }
        if (report[type] === undefined) {
          throw new Error('Unknown metric type ' + type);
        }

This way you only do the new TelemetryReport if it's actually needed and you only do it once