Graphs: Set ADJACENCY_LIST as default representation

alib2data/src/graph/directed/DirectedGraph.h

@@ -18,7 +18,7 @@ class IDirectedGraph;
 class DirectedGraph : public std::acceptor<DirectedGraph, VisitableGraphBase, std::acceptor<DirectedGraph, alib::VisitableObjectBase, GraphBase>>
 {
 public:
-	explicit DirectedGraph(REPRESENTATION representation);
+	explicit DirectedGraph(REPRESENTATION representation = REPRESENTATION::ADJACENCY_LIST);
 	~DirectedGraph() noexcept;
 	DirectedGraph(const DirectedGraph &other);

alib2data/src/graph/undirected/UndirectedGraph.h

@@ -18,7 +18,7 @@ class IUndirectedGraph;
 class UndirectedGraph : public std::acceptor<UndirectedGraph, VisitableGraphBase, std::acceptor<UndirectedGraph, alib::VisitableObjectBase, GraphBase>>
 {
 public:
-	explicit UndirectedGraph(REPRESENTATION representation);
+	explicit UndirectedGraph(REPRESENTATION representation = REPRESENTATION::ADJACENCY_LIST);
 	~UndirectedGraph() noexcept;
 	UndirectedGraph(const UndirectedGraph &other);