angular-formly: async select "loading" wrapper

Info: 

http://angular-formly.com/#/example/other/async-select-options-with-controller

`wrapper: 'loading',`

`
  app.run(function(formlyConfig) {
    formlyConfig.setWrapper({
      name: 'loading',
      templateUrl: 'loading.html'
    });
  });
`
