Added option to be able to change the size (aka height) of the panel.

* we provide the same 4 different sizes like at KDE3; Tiny (22px), Small (32px), Normal (48px, still default) and Large (64px)
* to call the "Configure Panel" dialog is a bit. Don't right-click on the panel itself since then the "Task manager Settings" are displayed, but click at e.g. the most top ~2pixel of the panel.
* this is work on progress and just an initial start to have that imho at least for small/wide-screen rather important option back.