VNCViewer: Hacky config variable (DontShowDialogs) to avoid showing any dialogs

[panreyes]

I added an option to avoid disabling any dialogs. I mostly wanted this to avoid getting messages if someone scanned my TCP/IP ports, but also to be able to check if the port is listening without triggering a dialog everytime.

The option name is DontShowDialogs.

Of course, this idea can be improved a lot, but this "hacky" variable is good enough for me.