added the create_notice_type wrapper in models

In the docs it is advised to use create_notice_type to create a new NoticeType object. But this function was absent. Although it is possible to create a new NoticeType using the 'create' function of the class, this addition makes the code follow the docs and compatible with previous code and other apps.

notification/models.py

@@ -24,6 +24,10 @@ class LanguageStoreNotAvailable(Exception):
     pass
 
 
+def create_notice_type(label, display, description, **kwargs):
+    NoticeType.create(label, display, description, **kwargs)
+
+
 class NoticeType(models.Model):
 
     label = models.CharField(_("label"), max_length=40)