TWizardNavigationEventParameter represents the parameter for
{@link TWizard}'s navigation events.
The index of the currently active step can be obtained from
{@link getCurrentStepIndex CurrentStepIndex}, while the index
of the candidate new step is in {@link getNextStepIndex NextStepIndex}.
By modifying {@link setNextStepIndex NextStepIndex}, the new step
can be changed to another one. If there is anything wrong with
the navigation and it is not wanted, set {@link setCancelNavigation CancelNavigation}
to true.