(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/common/delay.ts

@@ -0,0 +1,7 @@
+/**
+ * Returns a promise that resolves in the given number of milliseconds.
+ * (A replica of bluebird.delay using native promises.)
+ */
+export function delay(msec: number): Promise<void> {
+  return new Promise<void>((resolve) => setTimeout(resolve, msec));
+}