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:8000/js/examples/lib/hello_world/'

For dart:
- gulp examples/pub.serve
- open 'localhost:8080'
fix(class fields): handle untyped fields
feat(compiler): new semantics for `template` attributes and view variables.

- Supports `<div template=“…”>`, including parsing the expressions within
  the attribute.
- Supports `<template let-ng-repeat=“rows”>`
- Adds attribute interpolation (was missing previously)
feat(compiler): support events