Fixed multiple videos when autoplay on

For every user that joined the meeting,the autplay timer sent an
playStream event,starting a stream.The event should start only from the
presenter.
Fixed video resizing issues

- Fixed video resizing issues
- Correctly implemented video centering, now we center video both
vertically and horizontally when necessary
- Added a check to see if streams list is visible, if it is increase
video padding to account for the extra space