utility: Added Tracer for collecting time measurements

* define TRACING_ENABLED in utility/tracing.h to enable tracing
* invoke TraceEvent by writing TRACE() at start of function or scope
* provide an event name with TRACE("name")
* press SPACE to show collected traces history and report with accumulated times

src/lib_gui/qt/window/QtMainWindow.h

@@ -131,6 +131,7 @@ public slots:
 	void toggleView(View* view, bool fromMenu);
 
 	void handleEscapeShortcut();
+	void handleSpaceShortcut();
 
 	void updateRecentProjectMenu();
 
@@ -170,6 +171,7 @@ private:
 	QtWindowStack m_windowStack;
 
 	QShortcut* m_escapeShortcut;
+	QShortcut* m_spaceShortcut;
 };
 
 #endif // QT_MAIN_WINDOW_H