This fixes an issue with non-simulcast tracks being discarded
when bundled with simulcast tracks.

More explicit data structures, better error handling.

Firefox implements the spec correctly by encapsulatings received
data in a blob by default.  Handle both blobs and ArrayBuffers.

Also improve error handling.

We now distinguish between status, which is maintained by the server,
and data, which is provided by the client.  In addition to client data,
we now support group data.

Setting the status after joining (using the "setstatus" action)
may cause multiple "user" messages to be sent to clients.  Add
the ability to set the initial status at join time.

Commit 993d66 addes support for displaying raised hands, but it
failed to take into account the possibility that the hand is already
raised when the user is first added.

We're already doing it in the receiver loop.

Doing that at the sample level suffers from too much delay
due to buffering in the samplebuilder.

This fixes an issue with out-of-order packet's start flag not
being correctly set in all cases.

If the stream was very short, we may not have created
a writer yet.  Write out packets even in that case.

Apparently the field has a different name than the HTML attribute.

Chromium 91 and later uses "AV1" instead of "AV1X".  Simulcast is
still broken.

Show the "hand-paper" symbol instead of the "circle" symbol while a
user is raising their hand.

(*webClient).action may be called with the group mutex taken,
and therefore cannot take the client mutex.

This prevents simulcast from being switched on when we enable
recording.

We now request a keyframe if we lose too many packets.

This version fixes issues with out-of-order packets.