KitAreaWidget: fix crash on quit

Change-Id: I70145eae04f2fc885846215796e54578d7a9c897
Task-number: QTCREATORBUG-13258
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>
JsonWizard: Make bool values easier to work with in string expandsion

Return an empty string for "false".

Change-Id: I54506fb3db5857786c0448b0c76114ad237ef555
Reviewed-by: Daniel Teske <daniel.teske@digia.com>