Implement maySendNotifications based upon dnd work

src/vector/platform/ElectronPlatform.tsx

@@ -335,8 +335,8 @@ export default class ElectronPlatform extends VectorBasePlatform {
         return true;
     }
 
-    maySendNotifications(): boolean {
-        return true;
+    async maySendNotifications(): Promise<boolean> {
+        return this._ipcCall('getMaySendNotifications');
     }
 
     displayNotification(title: string, msg: string, avatarUrl: string, room: Room): Notification {

src/vector/platform/WebPlatform.ts

@@ -50,7 +50,7 @@ export default class WebPlatform extends VectorBasePlatform {
      * Returns true if the application currently has permission
      * to display notifications. Otherwise false.
      */
-    maySendNotifications(): boolean {
+    async maySendNotifications(): Promise<boolean> {
         return window.Notification.permission === 'granted';
     }