Proposal: Check availability of multiple Apps

[fahad19]

Currently

We can trigger something as soon as our desired App is available, via this API:

rootApp.getAppOnceAvailable$('SomeAppName')
  .subscribe(someApp => console.log(someApp));

Proposal

It would be handy if we can check the availability of multiple apps together:

rootApp.getAppOnceAvailable$(['SomeApp', 'AnotherApp'])
  .subscribe(function (someApp, anotherApp) {
    // fires once, when both `SomeApp` and `AnotherApp` are available
  });

[fahad19]

/cc @rbardini, @leandrooriente