* Further implementation of the yearl print style: Now the grid of days is already printed, non-working days are shaded a bit, and the day numbers are printed. No events are shown yet.
* Factor out the calls to draw the subheaders (weekdays in the weekstyle and month names in the yearstyle)
* Add a virtual int sortID(); method to the plugin base class. That value will be used (not implemented yet!) to identify the config pages in the widget stack and to sort the radio buttons in the style selection part of the print dialog.