Add upstream plugins

Signed-off-by: Adrian Nöthlich <git@promasu.tech>

wp-content/plugins/all-in-one-event-calendar/public/admin/themes-updated.php

@@ -0,0 +1,14 @@
+<div class="wrap">
+
+    <h2><?php _e( 'Update Calendar Themes', AI1EC_PLUGIN_NAME ); ?></h2>
+
+    <?php echo $msg; ?>
+
+    <?php if ( $errors ): ?>
+        <?php foreach ( $errors as $error ): ?>
+            <?php echo $error; ?>
+        <?php endforeach; ?>
+    <?php endif; ?>
+
+    <p><a class="button" href="<?php echo AI1EC_SETTINGS_BASE_URL; ?>"><?php _e( 'All-in-One Event Calendar Settings »', AI1EC_PLUGIN_NAME ); ?></a></p>
+</div>