Refactor the tree system

Each element of the tree now only has one parent, not a parent array.

- Creating an elements doesn't necessarily rely on an existing file
- Moving elements unregisters elements from the previous parent
- Moved some helpers to the builder instead of Entry

libs/Tree/Root.php

@@ -0,0 +1,15 @@
+<?php namespace Todaymade\Daux\Tree;
+
+class Root extends Directory
+{
+    /**
+     * The root doesn't have a parent
+     *
+     * @param Directory $uri
+     */
+    public function __construct($uri)
+    {
+        $this->setUri($uri);
+        $this->path = $uri;
+    }
+}