fix(aio): intercept all clicks on anchors

Previously we had the `LinkDirective` which intercepted clicks on anchors
outside the doc viewer. Now we intercept "all" link clicks within the app.

aio/src/testing/location.service.ts

@@ -5,6 +5,9 @@ export class MockLocationService {
   currentUrl = this.urlSubject.asObservable();
   search = jasmine.createSpy('search').and.returnValue({});
   setSearch = jasmine.createSpy('setSearch');
+  go = jasmine.createSpy('Location.go');
+  handleAnchorClick = jasmine.createSpy('Location.handleAnchorClick')
+      .and.returnValue(false); // prevent click from causing a browser navigation
   constructor(private initialUrl) {}
 }