Fix tasks persistence and display.

src/app/core/service/task.service.ts

@@ -7,7 +7,7 @@ import { TaskPersistenceService } from './task-persistence.service';
   providedIn: 'root'
 })
 export class TaskService {
-  _tasks: BehaviorSubject<Task[]> = new BehaviorSubject<Task[]>([]);
+  private _tasks: BehaviorSubject<Task[]> = new BehaviorSubject<Task[]>([]);
 
   constructor(
     private _taskPersistenceService: TaskPersistenceService
@@ -24,9 +24,15 @@ export class TaskService {
     const tasks = this._tasks.value;
     tasks.push(task);
     this._tasks.next(tasks);
+    this._saveTasks();
   }
 
-  _saveTasks(): void {
+  private _saveTasks(): void {
     this._taskPersistenceService.save(this._tasks.value);
   }
+
+  refresh() {
+    const tasks = this._taskPersistenceService.getAll();
+    this._tasks.next(tasks);
+  }
 }