Fixed sub-task handling

The previous implementation of sub-tasks did not work as expected: it
was possible to mark sub-tasks as completed before the parent task's
dependencies were satisfied. In addition, it was impossible to retrieve
a task's path from the database without running a recursive query.

Full paths to sub-tasks added to views, since it is now possible to
obtain them.

includes/t-data/item.inc.php

@@ -11,7 +11,8 @@ class Data_Item
 	public $depth;
 	public $lineage;
 
-	public $activeTasks;
+	public $activeTasks = 0;
+	public $activeTasksTotal = 0;
 	public $inactiveTasks;
 
 	public function __construct( $id , $name )