dispose method
Releases everything this controller owns. The page that created the controller calls this from its own
State.dispose(); a subclass that adds its own notifiers overrides this and ends with super.dispose().
Implementation
@override
void dispose() {
guestFilterController.dispose();
checkInController.dispose();
checkOutController.dispose();
guestCountController.dispose();
totalPriceController.dispose();
penaltyController.dispose();
guestNameController.dispose();
guestPhoneController.dispose();
notesController.dispose();
super.dispose();
}