(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/tmp.d.ts

@@ -0,0 +1,7 @@
+// Add declarations of the promisifies methods of tmp.
+import {Options, SimpleOptions} from "tmp";
+declare module "tmp" {
+  function dirAsync(config?: Options): Promise<string>;
+  function fileAsync(config?: Options): Promise<string>;
+  function tmpNameAsync(config?: SimpleOptions): Promise<string>;
+}