http://piwigo.org/bugs/view.php?id=2614 For themes creators.

On index.tpl, add

{if !empty($cats_navbar)}
  {assign var=navbar value=$cats_navbar}
  {include file='navigation_bar.tpl'|@get_extent:'navbar'}
{/if}

right after {$CATEGORIES}

And modify existing photos navbar by

{if !empty($thumb_navbar)}
  {assign var=navbar value=$thumb_navbar}
  {include file='navigation_bar.tpl'|@get_extent:'navbar'}
{/if}

http://piwigo.org/bugs/view.php?id=2781 For plugins creators.

Introduction of two template methods to add buttons to index and picture toolbars, allowing to place buttons relatively to each other :

$template->add_picture_button($content, $rank);
$template->add_index_button($content, $rank);

No changes for themes.