Add tags support

Set slugify to be global
Update modification date only if text has been changed
Fix a bug in preview (post_id was passed instead of blog_id)
Add Home, Category and Tag links in blog area instead of global area (dynastie template)
Fix a bug in Have_I_right

templates/tag.html

@@ -0,0 +1,13 @@
+{% extends "templates/base.html" %}
+
+{% block content %}
+{% if tags|length == 0 %}
+<b>Any tag available</b><br/><br/>
+{% else %}
+<table>
+{% for tag in tags %}
+    <tr><td>{{ tag.id }}</td><td>{{ tag.name }}</td><td><a href="/tag/edit/{{ tag.id }}">Edit</a></td><td><a href="/tag/delete/{{ tag.id }}">Delete</a></td></tr>
+{% endfor %}
+</table>
+{% endif %}
+{% endblock %}