[Galene] New protocol feature: client status

[Juliusz Chroboczek <jch@irif.fr>]

Dear all,

Due to popular demand, I've just added server-maintained application state
to Galène.  Every client now has a "status", which is maintained by the
server.  The server does not interpret the status, it just enforces
permissions.

The client status is an arbitrary JSON dictionary:

  {raisehand: true, mood: 'confused'}

A client can change their status by sending a "userAction" message of kind
"setstatus"; only the entries mentioned in the message are changed, the
others are left as they were.  Whenever the status of a user changes,
a "user" message of the right kind (usually "change") is broadcast, and
the "users" array reflects the new status.

The protocol is designed so that in the future it might be possible to
change other users' status, but this is not implemented yet -- you'll only
be able to change your own status for now.

While anything that can be done with status could in principle be done by
userMessages, Alain and I have found that this leads to useless
complication on the client side, so we've decided to maintain this small
piece of data in the server.

-- Juliusz