prevent zoom chat messages from stop working

[felippenardi]

This PR fixes two problems that was interrupting Social Stream on Zoom:

1- When a lot of messages are sent at once, the scroll stops and—because of the Zoom infinite scroll optimization—the messages doesn't appear on the HTML.

The fix for that was adding to the loop scroll down moviment, so that the chat always stay on the bottom

2- When someone shares the screen, the chat box closes and doesn't open afterwards, so messages stop appearing

The fix for that was adding to the loop tapping the "open chat" menu, that is only visible when it is closed

[steveseguin]

Thank you for the pull request; great stuff.