I20211001-1800
Uses PlainMessageDialog for the quit handler. Change-Id: Iab604bab060574893fa900ac52fab190f1172cae Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com> Reviewed-on: https://git.eclipse.org/r/c/pde/eclipse.pde.ui/+/186003 Tested-by: PDE Bot <pde-bot@eclipse.org>