utilize them_item_list for output in theme_chatroom_user_list - this should probably just go into drupalconlondon branch

I thought I had push access to chatroom.git repo (maybe my config is messed up, but I *am* able to push to nodejs.git properly), so I'm attaching my patch here for someone else to push up for me.

This patch just adjusts theme_chatroom_user_list so that it isn't hardcoding ul/li in a non-drupal way.

This should can probably just go into the drupalconlondon branch for now (d.o project-issue content types don't provide all the actual branches so i just picked "7.x-1.x-dev", but that's not what I coded against).