The login message is replaced with handshake, which only carries
the client id.  Username and password is now in the join message.
Permissions is replaced with joined.

Input elements have no contents.  Thanks to Antonin Décimo.

The best TSDoc type is (Text|HTMLElement)[], but to JSDoc the array is
not distributive. JSDoc prefers Text[]|HTMLElement[], but TSDoc
rejects that syntax. In the end, both are fine with
Array.<Text|HTMLElement>.

Also get rid of dead groups, they're not useful.

This was broken when we implemented local videos.

Don't attempt to present if we don't have the present permission,
don't display the friendly popup if we've selected presentation.

They now have the same format as chat messages; the only difference
is that they are not stored in the chat history.

Also adds userMessage method to ServerConnection.

Fix usermessages.

Thanks to Antonin Décimo.

Move custom video controls into its own function.  Remove some
DOM traversals, avoid querySelector.  Remove dead code.