Remove unescaped use of stream name in subscriptions page.

This was causing issues with our ability to unsubscribe from
streams with " in their names.

The solution here is a bit hacky, since it depends on the JavaScript
being fairly aware of the layout of the DOM, which is not great.
But it works.

This fixes Trac #328.

(imported from commit a1b6c8e1f3a9daacdc48920a195717aa89b3a9a9)

zephyr/jstemplates/subscription.html

@@ -8,8 +8,7 @@
   </td>
   <td class="span2">
     <button class="btn btn-block" type="button" name="subscription"
-            onclick="subs.unsubscribe('{{subscription}}');"
-            value="{{subscription}}">Unsubscribe</button>
+            onclick="subs.unsubscribe_button_click(event);">Unsubscribe</button>
   </td>
 </tr>
 {{/with}}

zephyr/static/js/subs.js

@@ -229,7 +229,8 @@ function ajaxSubscribe(stream) {
     });
 }
 
-exports.unsubscribe = function (stream) {
+exports.unsubscribe_button_click = function (e) {
+    var stream = $(e.target).parent().prev().find('.subscription_name').text();
     $.ajax({
         type: "POST",
         url: "/json/subscriptions/remove",