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/edit_tag.html

@@ -0,0 +1,9 @@
+{% extends "templates/base.html" %}
+
+{% block content %}
+<form action="/tag/edit/{{ tag.id }}" method="post">
+{% csrf_token %}
+{{ form.as_p }}
+<input type="submit" name="edit" value="Edit" /> <input type="submit" name="cancel" value="Cancel" />
+</form>
+{% endblock %}