(core) move client code to core

Summary:
This moves all client code to core, and makes minimal fix-ups to
get grist and grist-core to compile correctly.  The client works
in core, but I'm leaving clean-up around the build and bundles to
follow-up.

Test Plan: existing tests pass; server-dev bundle looks sane

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2627

stubs/app/server/lib/LoginSession.ts

@@ -5,7 +5,13 @@ import {ILoginSession} from 'app/server/lib/ILoginSession';
 export class LoginSession implements ILoginSession {
   public clients: Set<Client> = new Set();
   public async getEmail() {
-    return 'anon@getgrist.com';
+    return process.env.GRIST_DEFAULT_EMAIL || 'anon@getgrist.com';
+  }
+  public async getSessionProfile() {
+    return {
+      name: await this.getEmail(),
+      email: await this.getEmail(),
+    };
   }
   public async clearSession(): Promise<void> {
     // do nothing