Without this patch, changing the application color scheme from system
settings only affects some widgets. Notably, checkboxes highlighting
colors stays the old color, leading to a hodge-podge color scheme and
bad contrast on some items.
The breeze QStyle caches the colors read via KSharedConfig, so it needs
to re-read the configuration when the application color changes.
QApplication emits a signal (originating in KGlobalSettings), which we
can react to.
This fixes the coloring of various widgets in breeze right after color
Those I haven't tested, but look quite suspicious (so please re-test):