(core) Broadcast doc usage updates to clients

Summary:
Introduces a new message type, docUsage, that's broadcast to all connected
clients whenever document usage is updated in ActiveDoc.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3451

app/client/components/DocComm.ts

@@ -6,6 +6,7 @@ import {ActiveDocAPI, ApplyUAOptions, ApplyUAResult} from 'app/common/ActiveDocA
 import {DocAction, UserAction} from 'app/common/DocActions';
 import {OpenLocalDocResult} from 'app/common/DocListAPI';
 import {FilteredDocUsageSummary} from 'app/common/DocUsage';
+import {Product} from 'app/common/Features';
 import {docUrl} from 'app/common/urlUtils';
 import {Events as BackboneEvents} from 'backbone';
 import {Disposable, Emitter} from 'grainjs';
@@ -13,7 +14,6 @@ import {Disposable, Emitter} from 'grainjs';
 // tslint:disable:no-console
 
 export interface DocUserAction extends CommMessage {
-  docFD: number;
   fromSelf?: boolean;
   data: {
     docActions: DocAction[];
@@ -23,6 +23,13 @@ export interface DocUserAction extends CommMessage {
   };
 }
 
+export interface DocUsageMessage extends CommMessage {
+  data: {
+    docUsage: FilteredDocUsageSummary;
+    product?: Product;
+  };
+}
+
 const SLOW_NOTIFICATION_TIMEOUT_MS = 1000; // applies to user actions only
 
 /**