Fix top panel being hidden during pause mode following rP22957 / D2292 reported by Freagarach, ValihrAnt, Krinkle et al.

Remove the false misleading default.cfg z value that is always overwritten by CGUI::Xeromyces_ReadObject, both introduced in rP141.
Remove multiline property since its redundant with the default C++ boolean, making the default style more agnostic of final GUI Object classes.

Close advanced locale dialog correctly upon cancel following rP22676 / D1684.
Don't switch the background image when closing the credits dialog following rP17830, refs #3744.