Init headers in logging files. Clear logs each time outputLogs is enabled.

include/openspace/performance/performancemanager.h

@@ -77,10 +77,12 @@ public:
 
     PerformanceLayout* performanceData();
     void clearLogs();
+    void initLogs();
 
 private:
     bool _doPerformanceMeasurements;
     bool _loggingEnabled;
+    bool _clearLogs;
 
     std::string _logDir;
     std::string _prefix;