For several years distros patched startkde in several different ways,
every release, every new change on startdem to adapt as their needs.
To avoid this going further, this applies a simple sourcing schema where
every small step is ordered and sourced.
If distros desire to override or customize each step, just need create
a similar file under /etc/startkde.d/custom/<naming> and the script will
be overrided.

Signed-off-by: Helio Chissini de Castro <helio@kde.org>