Add DataStore (IndexedDB wrapper)

An alternative to the synchronous Settings API to work around storage
limitations of localStorage and allow  storing of arbitrarily large
data in form of most Javascript DataTypes,
see https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm#supported_types

src/api/index.ts

@@ -1,3 +1,4 @@
 export * as MessageEvents from "./MessageEvents";
 export * as Notices from "./Notices";
 export * as Commands from "./Commands";
+export * as DataStore from "./DataStore";