Add support for hashtag on user interface

Add migration to fix typo
Add support for linking hashtags with posts
Rework tag search page so it says a nicer message than page not found
when no post use that tag
Add new string to translation

templates/tags/index.html.tera

@@ -2,16 +2,22 @@
 {% import "macros" as macros %}
 
 {% block title %}
-{{ 'Articles tagged "{{ tag }}"' | _(tag=tag.tag) }}
+{{ 'Articles tagged "{{ tag }}"' | _(tag=tag) }}
 {% endblock title %}
 
 {% block content %}
-    <h1>{{ 'Articles tagged "{{ tag }}"' | _(tag=tag.tag) }}</h1>
+    <h1>{{ 'Articles tagged "{{ tag }}"' | _(tag=tag) }}</h1>
 
-    <div class="cards">
-        {% for article in articles %}
-            {{ macros::post_card(article=article) }}
-        {% endfor %}
-    </div>
+    {% if articles| length != 0 %}
+        <div class="cards">
+            {% for article in articles %}
+                {{ macros::post_card(article=article) }}
+            {% endfor %}
+        </div>
+    {% else %}
+        <section>
+            <h2>{{ "There is currently no article with that tag" | _ }}</h2>
+        </section>
+    {% endif %}
     {{ macros::paginate(page=page, total=n_pages) }}
 {% endblock content %}