Add solution for 2016 Day 24

src/common/lib/Graph.h

@@ -106,6 +106,11 @@ public:
     return graph.find(from)->second.find(to)->second;
   }
 
+  const std::map<Key, std::map<Key, Value>>& GetGraph() const
+  {
+    return graph;
+  }
+
   const std::map<Key, Value>& GetPaths(const Key& from) const
   {
     return graph.find(from)->second;