(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

stubs/app/server/server.ts

@@ -0,0 +1,25 @@
+import {updateDb} from 'app/server/lib/dbUtils';
+import {main as mergedServerMain} from 'app/server/mergedServerMain';
+import * as fse from 'fs-extra';
+
+const G = {
+  port: parseInt(process.env.PORT!, 10) || 8484,
+};
+
+export async function main() {
+  // Use a distinct cookie.
+  if (!process.env.GRIST_SESSION_COOKIE) {
+    process.env.GRIST_SESSION_COOKIE = 'grist_core';
+  }
+  // This is where documents are placed, for historic reasons.
+  await fse.mkdirp('samples');
+  // Make a blank db if needed.
+  await updateDb();
+  // Launch single-port, self-contained version of Grist.
+  // You probably want to have GRIST_DEFAULT_EMAIL set since there's no login system yet.
+  await mergedServerMain(G.port, ["home", "docs", "static"]);
+}
+
+if (require.main === module) {
+  main().catch((err) => console.error(err));
+}