Start a drag and drop implemntation for the lesson model/view.

Start a drag and drop implemntation for the lesson model/view.
Moving lessons around works, adding them as child has a tendency to add
the first instead of the selected lesson. Probably trivial.
Lots of cleanup.
WordType class has now always WordType as type, the special types are
handled in the class by a function.

svn path=/branches/work/kdeedu_parley/libkdeedu/; revision=748787