Event handler that will add new messages to the message log.

async def on_message(self, event):
        """
        Event handler that will add new messages to the message log.
        """
        # We want to show only messages sent to this chat
        if event.chat_id != self.chat_id:
            return

        # Save the message ID so we know which to reply to
        self.message_ids.append(event.id)

        # Decide a prefix (">> " for our messages, "<user>" otherwise)
        if event.out:
            text = '>> '
        else:
            sender = await event.get_sender()
            text = '<{}> '.format(sanitize_str(
                utils.get_display_name(sender)))

        # If the message has media show "(MediaType) "
        if event.media:
            text += '({}) '.format(event.media.__class__.__name__)

        text += sanitize_str(event.text)
        text += '\n'

        # Append the text to the end with a newline, and scroll to the end
        self.log.insert(tkinter.END, text)
        self.log.yview(tkinter.END)