provide easier chat reading for screen reader users in accessible chat activity

While the accessible version of the Chat activity is accessible, it could be more usable. The way to navigate the discussion is a bit cumbersome to listen to for screen reader users because of the use of definition lists.

It might be better to store the chat messages in a table with three columns. Column one would be a header column and include the poster's name. Column 2 would be the message. Column 3 would be the time stamp. This would allow screen reader users to simply navigate up and down the second column and easily hear the most pertinent information - the person's name and their message.

The current definition lists, while semantically correct, are quite verbose and cumbersome to navigate for screen reader users.