(core) Add new Grist login page

Summary:
Adds a new Grist login page to the login app, and replaces the
server-side Cognito Google Sign-In flow with Google's own OAuth flow.

Test Plan: Browser and server tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3332

app/server/lib/requestUtils.ts

@@ -68,8 +68,8 @@ export function addOrgToPath(req: RequestWithOrg, path: string): string {
 /**
  * Get url to the org associated with the request.
  */
-export function getOrgUrl(req: Request) {
-  return req.protocol + '://' + req.get('host') + addOrgToPathIfNeeded(req, '/');
+export function getOrgUrl(req: Request, path: string = '/') {
+  return req.protocol + '://' + req.get('host') + addOrgToPathIfNeeded(req, path);
 }
 
 /**