Refactor into testable concerns

[rall]

eg, in the google-map component this:

    /* track current and previous markers to identify by displaying info window */

    const identifyPair$:Observable<number[]> = this.clicks$.pipe(
      filter<ClickEvent>(event => event.event === "click"),
      map(evt => evt.index),
      debounceTime(200),
      startWith(-1),
      pairwise(),
      share(),
    );

    identifyPair$.pipe(
      filter(([previous, current]) => previous !== current),
      map(([previous]) => previous),
      selectIn(markerArray$),
      filterTrue<Marker>(),
      filter(marker => marker.isInfoWindowShown()),
    ).subscribe(marker => marker.hideInfoWindow());

    identifyPair$.pipe(
      map(([_, current]) => current),
      selectIn(markerArray$),
      filterTrue<Marker>(),
      filter(marker => !marker.isInfoWindowShown()),
    ).subscribe(marker => marker.showInfoWindow());

could be separated into an external, testable service