Feature/add gulp example

- Generate `lb-services.js` via `gulp-loopback-sdk-angular`
- Rebuild `lb-services.js` on changes in watch mode
- Minify javascript files
- Bundle javascript files into `bundle.js`
- Reminify and rebundle on changes in watch mode
That was the entire reason for leaving out build systems altogether from the beginning. Which is why I left all the build stuff under the `Optional` header.