[migration] fix handling of default value for boolean attributes
We can't assert that the old value is 'True' or 'False', because False
used to be stored as an empty string in pre-3.18 versions.
{% extends "basic/layout.html" %}
{% block header %}
<div class="header">
<a href="http://www.cubicweb.org">
<img alt="cubicweb logo" src="{{ pathto('_static/cubicweb.png', 1) }}"/>
</a>
</div>
{% endblock %}
{# puts the sidebar into "sidebar1" block i.e. before the document body #}
{% block sidebar1 %}{{ sidebar() }}{% endblock %}
{% block sidebar2 %}{% endblock %}