Add password-container and password-reset wrappers

This adds the wrappers necessary to center the content vertically and
horizontally within the page.

templates/zerver/reset_confirm.html

@@ -6,12 +6,14 @@
 
 {% block portico_content %}
 
-<div class="pitch">
+<div class="password-container">
+  <div class="password-reset">
+    <div class="pitch">
         <hr/>
         <h3>{{ _('Reset your password') }}.</h3>
-</div>
+    </div>
 
-{% if validlink %}
+    {% if validlink %}
         <form method="post" id="password_reset" class="form-horizontal">
         {{ csrf_input }}
             <div class="control-group">
@@ -56,11 +58,14 @@
             </div>
         </form>
 
-<script type="text/javascript">
+    <script type="text/javascript">
         autofocus('#id_new_password1');
-</script>
-{% else %}
+    </script>
+    {% else %}
         <p>{{ _('Sorry, the link you provided is invalid or has already been used') }}.</p>
-{% endif %}
+    {% endif %}
+
+  </div>
+</div>
 
 {% endblock %}