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

sites/blog.soutade.fr/_index.html

@@ -5,6 +5,7 @@
       <div class="post_sub_header">
 	<dyn:date/> | <div class="author_icon"> Écrit par <dyn:author/> </div>
       </div>
+      <dyn:tags link="1"/>
     </div>
     <dyn:post_content/>
   </dyn:posts>