Menu list is retrieved from the datasource in the init(SmappStateProcessingAction) method that is implemented by the subclass.
The menu list needs to be persisted into session attribute so that it can exist over multiple SMS sessions without reloading
it from the source (database or service). To persist the menu list using this method, the object in the list has to implement
BeanConverterInterface and Comparable.
This method is typically called from the init(SmappStateProcessingAction) method.