Asynchronous jobs (not the scheduling)

[Sergei Egorov]

Hi all,

I'm wondering if it's possible not to block the job executor's thread when
I wait for some async event.

somethingLike:

```
ignite.compute().run(() -> someServiceRefSomehow.doSomethingAsync());
```

where
```
interface SomeService {
    CompletableFuture<String> doSomethingAsync();
}
```

Or even better:

```
interface SomeService {
    Observable<String> doSomethingAsync();
}
```

Thanks!