Auto create super methods

When we override some Flutter life-cycle methods we have to always type a call to `super` and be aware if it's on the beginning or the end of the method, for example:

```dart
@override
void initState() {
super.initState();
// our code here
}

@override
void dispose() {
// our code here
super.dispose();
}
```

I think this could be automated when we use `Ctrl+O` to override the life-cycle methods, generating the overridden method, with the proper call to super and the caret at the right position.