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.

For es5:

- gulp build
- cd build/js
- python -m SimpleHTTPServer
- open 'localhost:8080/examples/lib/hello_world/'

For dart:

- gulp build
- cd build/dart/examples
- pub serve
- open 'localhost:8080'