added missing cancreate methods and property to StringTagField.

code/StringTagField.php

@@ -28,6 +28,11 @@ class StringTagField extends DropdownField
      */
     protected $lazyLoadItemLimit = 10;
 
+    /**
+     * @var bool
+     */
+    protected $canCreate = true;
+
     /**
      * @var null|DataObject
      */
@@ -343,4 +348,24 @@ class StringTagField extends DropdownField
     {
         return true;
     }
+
+    /**
+     * @return bool
+     */
+    public function getCanCreate()
+    {
+        return $this->canCreate;
+    }
+
+    /**
+     * @param bool $canCreate
+     *
+     * @return static
+     */
+    public function setCanCreate($canCreate)
+    {
+        $this->canCreate = $canCreate;
+
+        return $this;
+    }
 }