(core) move home server into core

Summary: This moves enough server material into core to run a home server.  The data engine is not yet incorporated (though in manual testing it works when ported).

Test Plan: existing tests pass

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2552

app/server/lib/GristServer.ts

@@ -0,0 +1,26 @@
+import {SessionUserObj} from 'app/server/lib/BrowserSession';
+import * as Comm from 'app/server/lib/Comm';
+import {Hosts} from 'app/server/lib/extractOrg';
+import {ICreate} from 'app/server/lib/ICreate';
+import {Sessions} from 'app/server/lib/Sessions';
+import * as express from 'express';
+
+/**
+ * Basic information about a Grist server.  Accessible in many
+ * contexts, including request handlers and ActiveDoc methods.
+ */
+export interface GristServer {
+  readonly create: ICreate;
+  getHost(): string;
+  getHomeUrl(req: express.Request, relPath?: string): string;
+  getHomeUrlByDocId(docId: string, relPath?: string): Promise<string>;
+}
+
+export interface GristLoginMiddleware {
+  getLoginRedirectUrl(target: URL): Promise<string>;
+  getSignUpRedirectUrl(target: URL): Promise<string>;
+  getLogoutRedirectUrl(nextUrl: URL, userSession: SessionUserObj): Promise<string>;
+
+  // Returns arbitrary string for log.
+  addEndpoints(app: express.Express, comm: Comm, sessions: Sessions, hosts: Hosts): string;
+}