(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/plugin/GristTable-ti.ts

@@ -0,0 +1,24 @@
+import * as t from "ts-interface-checker";
+// tslint:disable:object-literal-key-quotes
+
+export const GristTable = t.iface([], {
+  "table_name": t.union("string", "null"),
+  "column_metadata": t.array("GristColumn"),
+  "table_data": t.array(t.array("any")),
+});
+
+export const GristTables = t.iface([], {
+  "tables": t.array("GristTable"),
+});
+
+export const GristColumn = t.iface([], {
+  "id": "string",
+  "type": "string",
+});
+
+const exportedTypeSuite: t.ITypeSuite = {
+  GristTable,
+  GristTables,
+  GristColumn,
+};
+export default exportedTypeSuite;