ui: Group graph nodes by file or namespace (issues #171, #439, #522)

* added buttons to enable grouping by file or namespace
* last used group settings saved to ApplicationSettings
* made groups hoverable/clickable on label only
* improved node hatching and override edge colors
* group overview lists

fortune cookie message = Seen with the eyes of love, everything gets a new meaning.

src/lib/settings/ApplicationSettings.h

@@ -3,6 +3,7 @@
 
 #include <memory>
 
+#include "data/GroupType.h"
 #include "settings/Settings.h"
 
 class TimeStamp;
@@ -63,6 +64,9 @@ public:
 	bool getGraphControlsVisible() const;
 	void setGraphControlsVisible(bool visible);
 
+	GroupType getGraphGrouping() const;
+	void setGraphGrouping(GroupType type);
+
 	// screen
 	int getScreenAutoScaling() const;
 	void setScreenAutoScaling(int autoScaling);