[Fixed]-Template for reusable Django app is not rendering

The problem was in base.html template. There were such hrefs as <a href="{% url 'logout' %}">Выйти</a> and <a href="{% url 'login' %}">Войти</a>. Changing them to <a href="{% url 'guestbook:logout' %}">Выйти</a> and <a href="{% url 'guestbook:login' %}">Войти</a> solved the problem.