(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/lib/ServerLocale.ts

@@ -1,12 +1,12 @@
 import {parse as languageParser} from "accept-language-parser";
-import {Request} from 'express';
+import {IncomingMessage} from 'http';
 import {locales} from 'app/common/Locales';
 
 /**
  * Returns the locale from a request, falling back to `defaultLocale`
  * if unable to determine the locale.
  */
-export function localeFromRequest(req: Request, defaultLocale: string = 'en-US') {
+export function localeFromRequest(req: IncomingMessage, defaultLocale: string = 'en-US') {
   const language = languageParser(req.headers["accept-language"] as string)[0];
   if (!language) { return defaultLocale; }