Add navigation bar and fix the bug of "too many values to unbound"

templates/tag.html

@@ -1,6 +1,7 @@
 {% extends "templates/base.html" %}
 
 {% block content %}
+<a href="/blog/{{ blog.id }}?page=0">Home</a> <a href="/category/{{ blog.id }}">Categories</a> <a href="/tag/{{ blog.id }}">Tags</a><br/><br/>
 {% if tags|length == 0 %}
 <b>Any tag available</b><br/><br/>
 {% else %}