Add a model for router and change

Also adds a change-service, which maintains the change model.

The new router model is maintained by gr-router, which will eventually
be moved and renamed to router-service.

Change-Id: I15fcf39d1de21dea975a687fb6efb6823d658c22
diff --git a/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts b/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts
index 26368ec..973ccc8 100644
--- a/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts
+++ b/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts
@@ -25,7 +25,7 @@
 import {PolymerElement} from '@polymer/polymer/polymer-element';
 import {htmlTemplate} from './gr-change-list-view_html';
 import {page} from '../../../utils/page-wrapper-utils';
-import {GerritNav, GerritView} from '../../core/gr-navigation/gr-navigation';
+import {GerritNav} from '../../core/gr-navigation/gr-navigation';
 import {customElement, property} from '@polymer/decorators';
 import {AppElementParams} from '../../gr-app-types';
 import {
@@ -41,6 +41,7 @@
 import {ChangeListViewState} from '../../../types/types';
 import {fireTitleChange} from '../../../utils/event-util';
 import {appContext} from '../../../services/app-context';
+import {GerritView} from '../../../services/router/router-model';
 
 const LookupQueryPatterns = {
   CHANGE_ID: /^\s*i?[0-9a-f]{7,40}\s*$/i,