(core) Use new Banner component for activation messages

Summary: Use new Banner component for activation messages.

Test Plan: Existing tests.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3483

stubs/app/client/components/Banners.ts

@@ -0,0 +1,10 @@
+import {AppModel} from 'app/client/models/AppModel';
+import {DocPageModel} from 'app/client/models/DocPageModel';
+
+export function buildHomeBanners(_app: AppModel) {
+  return null;
+}
+
+export function buildDocumentBanners(_docPageModel: DocPageModel) {
+  return null;
+}

stubs/app/client/components/DocUsageBanner.ts

@@ -1,10 +0,0 @@
-import {DocPageModel} from 'app/client/models/DocPageModel';
-import {Disposable} from 'grainjs';
-
-export class DocUsageBanner extends Disposable {
-  constructor(_docPageModel: DocPageModel) { super(); }
-
-  public buildDom() {
-    return null;
-  }
-}