- on iOS safari and chrome, in case we show eg a spinner until we get the videoConferenceJoined event, all `clientResize` are done with size 0 for width/height
- on iOS we never get a `clientResize` call with correct values, except if we force a call by eg opening/closing the chat window

* ref(Filmstrip): Optimize resizes.

* fix(thumbnails): resize.

* fix(thumbnails): Issue with height 0, width 0.

* doc(Filmstrip): Improve JSDoc.

This refactors all handling of audio-only and last N to 2 features in preparation
for "low bandwidth mode".

The main motivation to do this is that lastN is a "global" setting so it helps
to have all processing for it in a single place.

left blank in default meet installations, to be overridden by adding <base href="CDN_URL"> to /base.html