- Initial proof of concept of modular startkde

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>