Fix HostingPlatform form

Now on `Project` deletion associated `ProjectHostingPlatform` object also will be deleted

templates/fossdb/add_project.html

@@ -6,6 +6,7 @@
     <form method="post">
         {% csrf_token %}
         {{ form.as_p }}
-        <button type="submit">Post</button>
+        {{ host_form.as_p }}
+        <button type="submit">Submit</button>
     </form>
 {% endblock %}