Oxygen: avoid calls to reparseConfiguration() on startup.

strace -e open kate |& grep -v NOENT | grep oxygenrc | wc -l
went from 8 to 4
(and when looking for kdeglobals, from 13 to 11)

There's still a lot of work to be done in that area...
(within KConfigSkeleton, and probably kdeplatformtheme)

REVIEW: 115964