limit rxjs imports

[Ks89]

limit rxjs imports, for example:

import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/combineLatest';
import 'rxjs/add/observable/throw';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';
import 'rxjs/add/operator/filter';
import 'rxjs/add/observable/from';
import 'rxjs/add/observable/fromEvent';
import 'rxjs/add/observable/interval';
import 'rxjs/add/operator/let';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/mapTo';
import 'rxjs/add/operator/mergeMap';
import 'rxjs/add/observable/of';
import 'rxjs/add/operator/pluck';
import 'rxjs/add/operator/sample';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/take';
import 'rxjs/add/operator/takeUntil';
import 'rxjs/add/operator/toArray';
import 'rxjs/ReplaySubject';
import 'rxjs/Observable';
import 'rxjs/Subject';
import 'rxjs/Subscription';