(core) Converting server-side Comm.js to typescript

Summary:
- Add app/common/CommTypes.ts to define types shared by client and server.
- Include @types/ws npm package

Test Plan: Intended to have no changes in behavior

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3467

app/server/declarations.d.ts

@@ -2,31 +2,6 @@ declare module "app/server/lib/ActionLog";
 declare module "app/server/lib/sandboxUtil";
 declare module "app/server/lib/User";
 
-declare module "app/server/lib/Comm" {
-  import {Client, ClientMethod} from "app/server/lib/Client";
-  import {ScopedSession} from "app/server/lib/BrowserSession";
-  import * as http from "http";
-
-  class Comm {
-    constructor(server: http.Server, options: any);
-    public broadcastMessage(type: string, messageData: any): void;
-    public destroyAllClients(): void;
-    public setServerVersion(serverVersion: string|null): void;
-    public setServerActivation(active: boolean): void;
-    public getSessionIdFromCookie(gristSidCookie: string): string;
-    public getOrCreateSession(sessionId: string, req: any): ScopedSession;
-    public registerMethods(methods: {[name: string]: ClientMethod}): void;
-    public getClient(clientId: string): Client;
-    public testServerShutdown(): Promise<void>;
-    public testServerRestart(): Promise<void>;
-    public testSetClientPersistence(ttlMs: number): void;
-  }
-  namespace Comm {
-    function sendDocMessage(client: Client, docFD: number, type: string, mesageData: any, fromSelf: boolean): void;
-  }
-  export = Comm;
-}
-
 declare module "app/server/lib/shutdown" {
   export function addCleanupHandler<T>(context: T, method: (this: T) => void, timeout?: number, name?: string): void;
   export function removeCleanupHandlers<T>(context: T): void;
@@ -91,9 +66,6 @@ declare module "app-module-path" {
   export function addPath(path: string): void;
 }
 
-// Used in tests
-declare module "ws";
-
 // version of pidusage that has correct ctime on linux
 declare module '@gristlabs/pidusage' {
   import * as pidusage from 'pidusage';