ui: separated GraphView style settings into class GraphViewStyle

This change adds the class GraphViewStyle that holds all values for defining the style of Nodes and Edges in the Graph.
The GraphViewStyleImpl interface and the QtGraphViewStyleImpl implementation are used to request Qt specific metrics,
like the charwidth of used fonts.

This change includes the following fixes:
* aggregation number always in the middle between nodes
* darker color for aggregation edge
* split off QGraphicsLineItem implementations from QtGraphEdge
* fixed some colors in color scheme

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src/lib/component/controller/GraphController.h

@@ -27,23 +27,6 @@ class GraphController
 	, public MessageListener<MessageGraphNodeMove>
 {
 public:
-	struct Margins
-	{
-		Margins();
-
-		int left;
-		int right;
-
-		int top;
-		int bottom;
-
-		int betweenX;
-		int betweenY;
-
-		int minWidth;
-		float charWidth;
-	};
-
 	GraphController(StorageAccess* storageAccess);
 	~GraphController();
 
@@ -70,12 +53,10 @@ private:
 	void layoutNesting();
 	void layoutNestingRecursive(DummyNode& node) const;
 
-	Margins getMarginsForDummyNode(DummyNode& node) const;
 	DummyNode* findDummyNodeRecursive(std::vector<DummyNode>& nodes, Id tokenId);
 	DummyNode* findDummyNodeAccessRecursive(std::vector<DummyNode>& nodes, Id parentId, TokenComponentAccess::AccessType type);
 
 	StorageAccess* m_storageAccess;
-	GraphView::Metrics m_viewMetrics;
 
 	std::vector<DummyNode> m_dummyNodes;
 	std::vector<DummyEdge> m_dummyEdges;