Add a dot exporter for the class graph

package es.upv.mist.slicing.cli;

import es.upv.mist.slicing.graphs.ClassGraph;

import org.jgrapht.nio.Attribute;

import org.jgrapht.nio.dot.DOTExporter;

import java.util.Map;

public class ClassGraphLog {

    protected DOTExporter<ClassGraph.Vertex<?>, ClassGraph.ClassArc> getDOTExporter() {

        DOTExporter<ClassGraph.Vertex<?>, ClassGraph.ClassArc> dot = new DOTExporter<>();

        dot.setVertexAttributeProvider(this::attributes);

        dot.setEdgeAttributeProvider(this::attributes);

        return dot;

    }

    protected Map<String, Attribute> attributes(ClassGraph.Vertex<?> vertex) {

        DOTAttributes res = new DOTAttributes();

        res.set("label", vertex.toString());

        return res.build();

    }

    protected Map<String, Attribute> attributes(ClassGraph.ClassArc arc) {

        DOTAttributes res = new DOTAttributes();

        return res.build();

    }

}

    /** A vertex containing the declaration it represents. It only exists because

     *  JGraphT relies heavily on equals comparison, which may not be correct in declarations. */

    protected static class Vertex<T extends BodyDeclaration<?>> {

    public static class Vertex<T extends BodyDeclaration<?>> {

        // First ancestor common class in the JavaParser hierarchy for

        // ClassOrInterfaceDeclaration, FieldDeclaration and CallableDeclaration

        protected final T declaration;

        }

    }

    protected static class ClassArc extends Arc {

    public static class ClassArc extends Arc {

        /** An arc that connects a class with another one that inherits from it. */

        protected static class Extends extends ClassArc {}

        /** An arc that connects an interface to a class that implements it. */