private void TomorrowSubmitButton_Click(object sender, EventArgs e)
        {
            PersonalTask task = new PersonalTask(tomorrowTaskText.Text, DateHandler.GetDateFromToday(1));

            AddTaskToListBox(task, TomorrowCheckedList);
        }
        private void TodaySubmitButton_Click(object sender, EventArgs e)
        {
            PersonalTask task = new PersonalTask(todayTaskText.Text, DateTime.Now);

            AddTaskToListBox(task, TodayCheckedList);
        }
        private void YesterdaySubmit_Click(object sender, EventArgs e)
        {
            PersonalTask task = new PersonalTask(yesterdayText.Text, DateHandler.GetDateFromToday(-1));

            AddTaskToListBox(task, YesterdayCheckedList);
        }
 void AddTaskToListBox(PersonalTask task, ListBox listBox)
 {
     listBox.Items.Add(task);
     Manager.History.AllTasks.Add(task);
 }