(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/BasketClientAPI.ts

@@ -0,0 +1,11 @@
+export interface BasketClientAPI {
+  /**
+   * Returns an array of all tableIds in this basket.
+   */
+  getBasketTables(): Promise<string[]>;
+
+  /**
+   * Adds, updates or deletes a table's data to/from Grist Basket.
+   */
+  embedTable(tableId: string, action: "add"|"update"|"delete"): Promise<void>;
+}