Initial commit of a pager applet.

The pager works in my setup and provides me with everything I use in KDE 3, including drag and drop of windows. I'm away next week and don't know how much time I'll have afterwards, so I'm just committing this now.

Issues:
* The pager doesn't use a DataEngine at the moment and I don't know if it's a good idea. I may make sense to extend the Tasks engine to provide the needed data, but the pager relies on different data like the stacking order.
* Updating and redrawing could be done in a better and more intelligent way.
* The colors are hardcoded and more or less random as I'm not an artist.
* More optional features like showing the window icons and different background modes could be implemented.
* I don't know if it works correctly in different setups (Beryl, Xinerama, ...).
* The applet "jumps" sometimes when changing the constraints or moving it.

This is the first thing I ever did with Plasma and just a couple of hours hacking, so I don't know if it's actually good enough. ;)