logic: Group nodes in inheritance graph who have the same base and derived nodes (issue #459)

* added graph node for grouping nodes with separate sub-layout
* group nodes show name in top left corner
* clicking on single edge activates source locations of all edges
* removed separate setters for token components
* fixed text nodes missing or too many in list layout
* moved simple row and column layouts to ListLayouter
* added skewed layout type to ListLayouter

fortune cookie message = Sometimes you should have the courage and risk something.

src/lib_gui/qt/view/graphElements/QtGraphNodeGroup.h

@@ -0,0 +1,33 @@
+#ifndef QT_GRAPH_NODE_GROUP_H
+#define QT_GRAPH_NODE_GROUP_H
+
+#include "data/NodeType.h"
+#include "qt/view/graphElements/QtGraphNode.h"
+
+class QGraphicsRectItem;
+class QtRoundedRectItem;
+
+class QtGraphNodeGroup
+	: public QtGraphNode
+{
+	Q_OBJECT
+public:
+	QtGraphNodeGroup(Id tokenId, const std::wstring& name, NodeType::GroupType type);
+	virtual ~QtGraphNodeGroup();
+
+	// QtGraphNode implementation
+	virtual bool isGroupNode() const;
+	virtual Id getTokenId() const;
+
+	virtual void updateStyle();
+
+private:
+	Id m_tokenId;
+	NodeType::GroupType m_type;
+
+	QtRoundedRectItem* m_background = nullptr;
+	QGraphicsRectItem* m_backgroundTopRight = nullptr;
+	QGraphicsRectItem* m_backgroundBottomLeft = nullptr;
+};
+
+#endif // QT_GRAPH_NODE_GROUP_H