add error handler pages for 400, 404, 500

incorporealcms/templates/base.html

@@ -12,6 +12,7 @@
 <link rel="icon" href="{{ url_for('static', filename='img/favicon.png') }}">
 
 <div class="site-wrap">
+    {% block header %}
     <div class="header">
         <div class="nav">
             {% for nav in navs %}
@@ -24,11 +25,14 @@
             <a href="?style=light">[light]</a>
         </div>
     </div>
+    {% endblock %}
+    {% block body %}
     <div class="content">
         {{ content }}
     </div>
     <footer>
         <i>Last modified: {{ mtime }}</i>
     </footer>
+    {% endblock %}
 </div>
 </html>