feat(examples): adds hello-world app.

The app is writen in ES6 and transpiles to ES5 and dart as part of the
usual build.

The app contains a component, a directive and a services wired together
through dependency injection.

Before Each:
- gulp build

For es5:
- gulp serve
- open 'localhost:8080/js/examples/lib/hello_world/'

For dart:
- gulp examples/pub.serve
- open 'localhost:8080'
Delete `examples/todo`