Make storage stats consistent

static/index.html

@@ -2,8 +2,8 @@
 <p>Archived {{message_count}} messages from {{user_count}} users across {{channel_count}} channels on {{server_count}} servers.</p>
 <h3>Storage usage</h3>
 <dl>
-    <dt>Total archive</dt><dd>{{total_storage}}</dd>
-    <dt>Messages and metadata</dt><dd>{{message_storage}}</dd>
+    <dt>Archived data</dt><dd>{{total_storage}}</dd>
+    <dt>Message content</dt><dd>{{message_storage}}</dd>
     <dt>Attachments</dt><dd>{{attachment_storage}}</dd>
 </dl>