docs: def get_template(cls, message, messenger):
          """Get a template path to compile a message.
  
          1. `tpl` field of message context;
          2. `template` field of message class;
          3. deduced from message, messenger data and `template_ext` message type field
             (e.g. `sitemessage/messages/plain__smtp.txt` for `plain` message type).
  
          :param Message message: Message model
          :param MessengerBase messenger: a MessengerBase heir
          :return: str
          :rtype: str
          """
          template = message.context.get('tpl', None)
  
          if template:  # Template name is taken from message context.
              return template
  
          if cls.template is None:
              cls.template = 'sitemessage/messages/%s__%s.%s' % (
                  cls.get_alias(), messenger.get_alias(), cls.template_ext
              )
          return cls.template