jpackage: uniform error messages on different platforms

[Jon Harper]

when things go wrong launching an app packaged with jpackage, the
behavior is different accross platform:
- on windows it show a popup
- on other platforms it logs to stdout

I think it would be better if the behavior was consistent:
- provide popups on other platforms when the program is launched from
a file explorer
- provide messages on the console on windows when there is one.

Maybe all this can be autodetected, or maybe it should there should be
a global --console (like --winconsole today) that cotnrols how the
error messages are displayed ?

Cheers,
Jon