Add 'success' virtual field to the tasks

src/tasks.js

@@ -77,7 +77,9 @@ function get(id, callback) {
         if (error && error.reason == DatabaseError.NOT_FOUND) return callback(new TaskError(TaskError.NOT_FOUND));
         if (error) return callback(new TaskError(TaskError.INTERNAL_ERROR, error));
 
+        // add some virtual fields
         task.active = !!gTasks[id];
+        task.success = task.percent === 100 && !task.errorMessage;
 
         callback(null, task);
     });