aggregator2: add a hook to display a link to the aggregator2 page from the Federation tab.

modules/aggregator2/hooks/hook_frontpage.php

+<?php
+/**
+ * Hook to add the aggregator2 lik to the frontpage.
+ *
+ * @param array &$links The links on the frontpage, split into sections.
+ */
+function aggregator2_hook_frontpage(&$links) {
+    assert('is_array($links)');
+    assert('array_key_exists("links", $links)');
+
+    $links['federation'][] = array(
+        'href' => SimpleSAML_Module::getModuleURL('aggregator2/'),
+        'text' => '{aggregator2:aggregator:frontpage_link}',
+    );
+
+}