[MIG] web_notify: Migration to 12.0

Add self-test buttons in demo environment,
Updated readme to show how to test it.
Add buttons to users form
Do not rely on SUPERUSER_ID and avoid getattr usage

web_notify/readme/USAGE.rst

@@ -0,0 +1,23 @@
+
+To send a notification to the user you just need to call one of the new methods defined on res.users:
+
+.. code-block:: python
+  
+   self.env.user.notify_info(message='My information message')
+
+or 
+
+.. code-block:: python
+  
+   self.env.user.notify_warning(message='My marning message')
+
+.. figure:: static/description/notifications_screenshot.png
+   :scale: 80 %
+   :alt: Sample notifications
+
+You can test the behaviour of the notifications by installing this module in a demo database.
+Access the users form through Settings -> Users & Companies. You'll see a tab called "Test web notify", here you'll find two buttons that'll allow you test the module.
+
+.. figure:: static/description/test_notifications_demo.png
+   :scale: 80 %
+   :alt: Sample notifications