(core) move data engine code to core

Summary:
this moves sandbox/grist to core, and adds a requirements.txt
file for reconstructing the content of sandbox/thirdparty.

Test Plan:
existing tests pass.
Tested core functionality manually.  Tested docker build manually.

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2563

sandbox/install_tz.js

@@ -0,0 +1,31 @@
+const path = require('path');
+require('app-module-path').addPath(path.dirname(__dirname));
+require('ts-node').register();
+
+/**
+ * This script converts the timezone data from moment-timezone to marshalled format, for fast
+ * loading by Python.
+ */
+const marshal = require('app/common/marshal');
+const fse = require('fs-extra');
+const moment = require('moment-timezone');
+const DEST_FILE = 'sandbox/grist/tzdata.data';
+
+function main() {
+  const zones = moment.tz.names().map((name) => {
+    const z = moment.tz.zone(name);
+    return marshal.wrap('TUPLE', [z.name, z.abbrs, z.offsets, z.untils]);
+  });
+  const marshaller = new marshal.Marshaller({version: 2});
+  marshaller.marshal(zones);
+  const contents = marshaller.dumpAsBuffer();
+
+  return fse.writeFile(DEST_FILE, contents);
+}
+
+if (require.main === module) {
+  main().catch((e) => {
+    console.log("ERROR", e.message);
+    process.exit(1);
+  });
+}