(core) Simple localization support and currency selector.

Summary:
- Grist document has a associated "locale" setting that affects how currency is formatted.
- Currency selector for number format.

Test Plan: not done

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D2977

app/common/schema.ts

@@ -9,6 +9,7 @@ export const schema = {
     basketId            : "Text",
     schemaVersion       : "Int",
     timezone            : "Text",
+    documentSettings    : "Text",
   },
 
   "_grist_Tables": {
@@ -182,6 +183,7 @@ export interface SchemaTypes {
     basketId: string;
     schemaVersion: number;
     timezone: string;
+    documentSettings: string;
   };
 
   "_grist_Tables": {