Xpra: Ticket #625: a server event interface

So the server can expose important session events:

new clients connecting
client disconnected
lost connection events
first UI event (sent when the first window or tray is sent to the client
startup complete (sent when all the windows and trays have been sent to the client after it connects - can precede first UI event if there are no windows to forward)
server exit events (shutdown, etc)

If might make sense to expose this via dbus, but the easiest thing to do initially is probably to just add this interface to xpra's own channel.

Implemented in r7116 (see commit message for details).

Try it with the new hidden command _monitor:

xpra _monitor :DISPLAY

If that works for you, let me know what other events we can add, the only events you will get right now are:

handshake-complete when we accept a connection
startup-complete: uuid when the client has received all the windows
connection-lost: uuid when the client connection is lost (for whatever reason)

We could add:

first-ui-event (though at the moment this one is done client side, so the logic would have to be replicated server side, no biggie)
disconnect events so we know when the client exited cleanly rather a lost connection

and more..

Should be closed for v0.14.x, raising to critical.

Should be closed against milestone 0.14

Bump!

Unless anything is still missing, please close.