Added const to Array.GetSize(), and to 3 Node methods.

src/Array.cpp

@@ -141,9 +141,9 @@ void Array::Remove(unsigned int pos)
     _array.erase(it);
 }
 
-unsigned int Array::GetNodeIndex(Node* node)
+unsigned int Array::GetNodeIndex(Node* node) const
 {
-    std::vector<Node*>::iterator it = std::find(_array.begin(), _array.end(), node);
+    std::vector<Node*>::const_iterator it = std::find(_array.begin(), _array.end(), node);
     return std::distance (_array.begin(), it);
 }