title: Promise .all() with RxJS
body: <p>I'm writing an app in Angular 2 and I want to execute several http requests and run a function on the responses.</p>
  
  <p>In Angular 1, I would write something like <code>$q.all([$http.get(...), $http.get(...), ...]).then(doSomethingWithResponses);</code></p>
  
  <p>But Angular 2 returns RxJS Observables and after a bunch of reading I still can't figure out how to get the responses of several http requests.  How can this can be done?</p>