'Register a message to be shown to the user in the next page.
Arguments:
message_type (UserMessageType): the user message type
body_html (str): body of the message in html format
title (str): optional title for the message as plain text'

@classmethod
def register_user_message(self, request, message_type, body_html, title=None):

    assert isinstance(message_type, UserMessageType)
    message = Text(self.get_message_html(body_html, title))
    messages.add_message(request, message_type.value, Text(message), extra_tags=self.get_namespace())
