Update PostModifyForm to use permissions to create its fields

Fields are only displayed via the PostModifyForm if the user has
specific permissions to do things, like set stickies.

Also, add PostModifySuccessView that will close the modify window when
the process is complete.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

board/templates/board/base.html

@@ -12,8 +12,11 @@
         <script src="{% static 'board/jquery.js' %}"></script>
         <script src="{% static 'board/jsframe.min.js' %}"></script>
         <script src="{% static 'board/post.js' %}"></script>
-        {% if perms.board.create_ban %}
-            <script src="{% static 'board/ban_window.js' %}"></script>
+        {% if perms.board.add_ban %}
+            <script src="{% static 'board/ban.js' %}"></script>
+        {% endif %}
+        {% if can_modify %}
+            <script src="{% static 'board/modify.js' %}"></script>
         {% endif %}
         {% block extrajs %}{% endblock %}
     </head>