ui: Added custom trail dialog (issue #249)

* open custom trail dialg via button in top of trail controls
* search from symbol to symbol or all referenced/referencing of symbol
* define search depth with slider
* define horizontal/vertical layout
* define node and edge types
* renamed depth graph to trail in graph ui
* added custom trail UI tests

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testing/graph_view/data/custom_trail_files/custom.h

@@ -0,0 +1,56 @@
+void func()
+{
+	int m;
+}
+
+void func2()
+{
+	func();
+}
+
+class CustomA
+{
+public:
+	void method()
+	{
+		func();
+	}
+
+	int i;
+};
+
+class CustomB
+{
+public:
+	void method()
+	{
+		a.method();
+	}
+
+	CustomA a;
+};
+
+class CustomC
+{
+public:
+	int method()
+	{
+		func2();
+		bool a;
+		char c;
+	}
+
+	CustomA a;
+};
+
+class CustomD
+{
+public:
+	void method()
+	{
+		b.method();
+	}
+
+	CustomB b;
+	CustomC c;
+};