Initial commit for new screenlocker

The screen locker is split into two parts:
1. A daemon (ksld) to just lock the screen and grab input
2. An unlock dialog (kscreenunlocker) which is executed as a separate
process.

In case the unlocker fails/crashes the screen is still locked by
the lock daemon. The lock daemon uses an X event filter to ensure
that it's lock window and all unlocker windows are always on top.
All input events are passed to the correct unlocker window.

In case kscreenunlocker crashes or does not succeed, it gets
automatically restarted by the daemon.