Add pass templates listing

It's now possible to get the list of created passes templates.

* New method : listTemplates

src/PassSlot.php

@@ -1,4 +1,5 @@
 <?php
+
 /**
  * Licensed under the Apache License, Version 2.0 (the "License"); you may
  * not use this file except in compliance with the License. You may obtain
@@ -182,6 +183,16 @@ public function listPasses($passType = null) {
            }
            return $this->_restCall("GET", $resource);
        }
+
+        /**
+        * Returns descriptions of all created passes templates
+        * 
+        * @return array
+        */
+       public function listTemplates() {
+           $resource = "/templates";
+           return $this->_restCall("GET", $resource);
+       }
 
 	/**
 	 * Downloads the pkpass file