test(rxModalAction): Page objects, tests.

At least in this example, I don't like that this makes the chai-as-promised assertions looks confusing

```
expect(somePromise()).to.eventually.be.displayed;
```

I'd look at that and think that the result of `somePromise` alters the UI in a way that isn't immediate right away, but *eventually*, instead of talking about unwrapping a promise call one level for you.