Adds SailorConsumer Widget

[hjJunior]

This PR is a MVP of #10, which will allow users to use SailorConsumer as a Builder

Example

class PageWithSailorConsumer extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return SailorConsumer<ThirdPageArgs>(
      builder: (context, ThirdPageArgs arg) {
        return Scaffold(
          appBar: AppBar(
            title: Text('Using SailorConsumer'),
          ),
          body: Text('Count arg: ${arg.count}'),
        );
      },
    );
  }
}

I also added this to example folder

[pishguy]

when this PR can be merge?