fix(tooltip): properly position tooltips close to container edges

Fixes #1263
Fixes #1371
Closes #1643

src/tooltip/tooltip.ts

@@ -118,6 +118,11 @@ export class NgbTooltip implements OnInit, OnDestroy {
         window.document.querySelector(this.container).appendChild(this._windowRef.location.nativeElement);
       }
 
+      // position tooltip along the element
+      positionElements(
+          this._elementRef.nativeElement, this._windowRef.location.nativeElement, this.placement,
+          this.container === 'body');
+
       // we need to manually invoke change detection since events registered via
       // Renderer::listen() - to be determined if this is a bug in the Angular itself
       this._windowRef.changeDetectorRef.markForCheck();