Hardcoded meta viewport; CSS to fix vertical whitespace forcing scrollbar

Viewport meta tag should be the same on all platforms, so can remove from apprtc.py and hardcode in index.html.

`font-size: 0` on div#videos is to remove extra vertical whitespace that causes scrollbars. #localVideo and #remoteVideo have `height:100%`, so any whitespace between elements in HTML is treated as additional vertical whitespace :^/. A bit of a hack – alternatives welcome.

@juberti PTAL.