Changed chat behaviour

added recoil value isMobile to determine which chat to display and
style. #1978

changed the player to actually span across the viewport without the
black borders around it.

web/stories/ChatContainer.stories.tsx

@@ -38,6 +38,7 @@ const AddMessagesChatExample = args => {
         usernameToHighlight={null}
         chatUserId={null}
         isModerator={false}
+        isMobile={false}
       />
     </div>
   );