Bug 1104731 - [Rooms] Move 'feedback' screen code to a reusable componen...

...t r=crdlc
if (document.querySelector('#' + PANELS_ID. create_room)) exits you don't have to create again the panel and linkg but you have to execute HtmlImports.populate(function() {.. to know when resources were loaded. Otherwise the promise is not resolved with this return. And if you execute return Promise.resolve(xx) you don't have the xx object