rxjs slim import

I notice there are code where rxjs Subject and Observable are imported, they're being brought in from 'rxjs/Rx'

`import { Subject, Observable } from 'rxjs/Rx';`

Is there a reason these can't be brought in from their respective areas within rxjs?

```
import { Subject } from 'rxjs/Subject';
import { Observable } from 'rxjs/Observable';
```

I've found that with this change, webpack-dev-server reports the main.bundle is 945k, whereas it was 1.53 MB when using the single line include (packaging much more than just Subject and Observable).

I'm presently trying to consume ng2-smart-table as a package within another project and noticed while trying to profile my webpack builds that all of rxjs seemed to be included somewhere.