Added function sayByeBye() to command server.
Added test call to sayByeBye() from command panel when disconnected.
Redefined toString in Bye command.
Implemented handle bye command in central station handler.
Added handling Bye command ack in command station connected handler (received when sending directly bye without previous disconnect).
Changed in command station notConnected handler: do not respond to isAlive sent by drone.
Changed command station isAlive response in HandlerConnected: respond only to central station or drone to which command station is connected.