[startkde] Move more logic into startplasma-wayland from waylandsession

startplamsa-wayland and startplasma-waylandsession are split so that
anything requiring an X or wayland connection happens in
startplasma-waylandsession anything else can happen in the first binary.

runStartupConfig and setting an env variable can happen before kwin. It
might even fix a bug if kwin used any calls that rely on QLocale.