(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/gen-server/migration/1573569442552-CustomerIndex.ts

@@ -0,0 +1,15 @@
+import {MigrationInterface, QueryRunner, TableIndex} from "typeorm";
+
+export class CustomerIndex1573569442552 implements MigrationInterface {
+
+  public async up(queryRunner: QueryRunner): Promise<any> {
+    await queryRunner.createIndex("billing_accounts", new TableIndex({
+      name: "billing_accounts__stripe_customer_id",
+      columnNames: ["stripe_customer_id"]
+    }));
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<any> {
+    await queryRunner.dropIndex("billing_accounts", "billing_accounts__stripe_customer_id");
+  }
+}