Improve Modello model documentation: fields order is counter intuitive

In actual Modello model's documentation, name, description, comment and version elements are documented at the end of every structure (interfaces, classes or fields): that's counter intuitive.
As these are actually the most important informations, it would be a lot more intuitive to have them at the beginning of these structures.

Analysis: this is due to the fact that these fields are inherited from a base class.
Now that MODELLO-224 has been done, having the order we want is not a problem any more: just eat our own dogs' food