The function filter_special_chars does not have to throw a TypeError
when its argument text is null or undefined because (1) it can be argued
that neither of these two contains special characters and (2) it is much
more convenient to have the check in the function in question rather at
its multiple call sites.

Rename variables with "stream" in name which refer to JitsiTrack.
Rename TRACK ADDED/REMOVED events.
Try to reduce direct access to remoteTracks object.
Log warning message when track is overwritten.

We were assigning the var, before the type was compared which
could result in accepting "audio" stream for "video" JitsiLocalTrack.

Setting the `src` of a video element to null triggered a network request for resource "null".