nogui: don't zombie on suspend. --noguiprompt to prompt before exit

when running with --nogui, PCSX2 knows to exit when the GS window closes.
However, pressing esc (suspend) didn't close the window and instead hidden it.
As a result, PCSX2 didn't exit and remained a zombie process.

this patch closes the gs window on suspend in --nogui mode, which makes PCSX2
exit fully.

it's now also possibly to use --noguiprompt which prompts if esc will exit
PCSX2, and allows the user to abort the suspend and continue using PCSX2.

TODO: if PCSX2 was in full screen - then pressing esc exits full screen. it
would have been ideal to restore full screen, but for now it doesn't.