Nodes - Implemented saving/loading

Nodes - Added data model node

src/Artemis.Core/Extensions/IEnumerableExtensions.cs

@@ -92,5 +92,17 @@ namespace Artemis.Core
                 }
             }
         }
+
+        public static int IndexOf<T>(this IReadOnlyCollection<T> self, T elementToFind)
+        {
+            int i = 0;
+            foreach (T element in self)
+            {
+                if (Equals(element, elementToFind))
+                    return i;
+                i++;
+            }
+            return -1;
+        }
     }
 }