def create_message(self, level, msg_text, extra_tags, date=None):
raise NotImplementedError()<EOL>
Create and return a `Message` instance.
Instance types depend on backends implementation.

Params:
    `level`: message level (see django.contrib.messages)
    `msg_text`: what you think it is
    `extra_tags`: see django.contrib.messages
    `date`: a DateTime (optional)

Return:
    `Message` instance