TutorialItem::Indentifier param of init method should be optional

[gerchicov-bp]

What if I don't need to declare identifier at once in init method?

For example I need to create an array of items first and only then I want to assign identifiers because I could do it in for loop without hardcoding each next event handler.

And finally of course you made identifier readonly a constant to prevent its future changes. WHY?