Give priority to ATOM to expose WebSub.

Hello,
The ATOM feed contains the hub declaration for WebSub / PubSubHubbub, but the RSS / RDF / JSON versions do not.
Currently, the ATOM version is declared last.
RSS/ATOM clients typically pick whichever version comes first, and will thus not see the WebSub feature.
I therefore suggest putting the ATOM version first, as it is more feature-rich than the other versions.

Clients not compatible with ATOM would not pick it anyway due to the different type attribute.

See same PR for Mastodon: mastodon/mastodon#9302
and WebSub tester https://websub.rocks/publisher

actions/public.php

@@ -97,23 +97,23 @@ function showSections()
      */
     function getFeeds()
     {
-        return array(new Feed(Feed::JSON,
+        return array(new Feed(Feed::ATOM,
+                              common_local_url('ApiTimelinePublic',
+                                               array('format' => 'atom')),
+                              // TRANS: Link description for public timeline feed.
+                              _('Public Timeline Feed (Atom)')),
+                    new Feed(Feed::JSON,
                               common_local_url('ApiTimelinePublic',
                                                array('format' => 'as')),
                               // TRANS: Link description for public timeline feed.
                               _('Public Timeline Feed (Activity Streams JSON)')),
                     new Feed(Feed::RSS1, common_local_url('publicrss'),
                               // TRANS: Link description for public timeline feed.
                               _('Public Timeline Feed (RSS 1.0)')),
-                     new Feed(Feed::RSS2,
+                    new Feed(Feed::RSS2,
                               common_local_url('ApiTimelinePublic',
                                                array('format' => 'rss')),
                               // TRANS: Link description for public timeline feed.
-                              _('Public Timeline Feed (RSS 2.0)')),
-                     new Feed(Feed::ATOM,
-                              common_local_url('ApiTimelinePublic',
-                                               array('format' => 'atom')),
-                              // TRANS: Link description for public timeline feed.
-                              _('Public Timeline Feed (Atom)')));
+                              _('Public Timeline Feed (RSS 2.0)')));
     }
 }