first commit : grave core and admin plugin

system/src/Grav/Common/GPM/AbstractCollection.php

@@ -0,0 +1,32 @@
+<?php
+namespace Grav\Common\GPM;
+
+use Grav\Common\GravTrait;
+use Grav\Common\Iterator;
+
+abstract class AbstractCollection extends Iterator {
+
+    use GravTrait;
+
+    public function toJson()
+    {
+        $items = [];
+
+        foreach ($this->items as $name => $package) {
+            $items[$name] = $package->toArray();
+        }
+
+        return json_encode($items);
+    }
+
+    public function toArray()
+    {
+        $items = [];
+
+        foreach ($this->items as $name => $package) {
+            $items[$name] = $package->toArray();
+        }
+
+        return $items;
+    }
+}