Update outdated and broken holiday stylesheets
Each style was updated by copying qt.css and then adjusting
the required definitions such as background image and color.
foreach(dir
British
Classic
Default
Default_es
Default_pl
Default_ru
Default_uk
HillBilly
Mobster
Pirate
Robot
Russian
Russian_pl
Singer
Surfer
)
add_subdirectory(${dir})
endforeach(dir)