added classes config parameter

This allows users to set custom CSS classes on aggregations potentially
restyling them differently for different use cases.

This makes startScope and finishScope part of the public API of the
Aggregation class. It should no longer be called within render() but is
instead called outside.

This might potentially break plugins implementing their own
aggregations. Needs to be checked

syntax/table.php

@@ -117,7 +117,9 @@ class syntax_plugin_struct_table extends DokuWiki_Syntax_Plugin
 
             /** @var Aggregation $table */
             $table = new $this->tableclass($mainId, $format, $renderer, $search);
+            $table->startScope();
             $table->render(true);
+            $table->finishScope();
 
             if ($format === 'metadata') {
                 /** @var Doku_Renderer_metadata $renderer */