Fixed E_NOTICE in listing worker queue and new utilities class added (#5521)

* Fixes for E_NOTICE in workqueue:
- introduced class `Friendica\Util\Arrays` which will hold static methods for
  handling arrays that cannot be done with PHP's functions, like implode() on
  multi-dimensional arrays
- rewrote old-school for() loop to foreach()

* Added intial unit test with some tests on empty delimiters and/or sinle and
multi-dim array.

* Added test for for 3-dimensional arrays, thanks to  nupplaphil's feedback.

mod/admin.php

@@ -21,6 +21,7 @@ use Friendica\Model\Item;
 use Friendica\Model\User;
 use Friendica\Module\Login;
 use Friendica\Module\Tos;
+use Friendica\Util\Arrays;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Temporal;
 
@@ -783,9 +784,9 @@ function admin_page_workerqueue(App $a)
 	$statement = DBA::select('workerqueue', ['id', 'parameter', 'created', 'priority'], ['done' => 0], ['order'=> ['priority']]);
 	$r = DBA::toArray($statement);
 
-	for($i = 0; $i < count($r); $i++) {
+	foreach ($r as $key => $rr) {
 		// fix GH-5469. ref: src/Core/Worker.php:217
-		$r[$i]['parameter'] = implode(json_decode($r[$i]['parameter'], true), ': ');
+		$r[$key]['parameter'] = Arrays::recursiveImplode(json_decode($rr['parameter'], true), ': ');
 	}
 
 	$t = get_markup_template('admin/workerqueue.tpl');