Aggiunte e modifiche per lower_body

src/collections/headers/collection_interface.hpp

@@ -17,4 +17,15 @@ class CollectionInterface{
 };
 
 
-#endif
+#endif
+
+inline collection operator+(collection c1, collection c2){
+    collection res;
+    for (PieceInterface* i : c1.pieces){
+        res.pieces.push_back(i);
+    }
+    for (JointInterface* i : c1.joints){
+        res.joints.push_back(i);
+    }
+    return res;
+}