GDA-5877 Improve Linux launchers for stopping/restarting example GDA servers

The stop script is pretty much as it was, but for restarting, we now:
 * stop all servers
 * start name server, event server, log server in the background
 * start object server in the foreground

By running the object server in the foreground, the script itself continues to
run while the object server is running, so we see the object server's output
in Eclipse.