Display whether a message is historical in the actions popover.

I made this a smaller font size since it's kinda a footnote.

(imported from commit 2ad561e9fd1434d5dd19fa8c947fbc5185d71586)

zephyr/static/styles/zephyr.css

@@ -388,6 +388,10 @@ td.pointer {
     font-size: 90%;
 }
 
+.small {
+    font-size: 80%;
+}
+
 .actions_hovered .message_time {
     color:           #0088CC;
     text-decoration: underline;

zephyr/static/templates/actions_popover_content.handlebars

@@ -7,6 +7,9 @@
 
     <li>{{message.full_date_str}}</li>
     <li>{{message.full_time_str}}</li>
+    {{#if message.historical}}
+    <li class="small">(Message sent when you were not subscribed)</li>
+    {{/if}}
     <hr />
   </div>