Simple fix for bug 16848 - added ::mitk:: prefix where necessary

Signed-off-by: Rostislav Khlebnikov <r.khlebnikov@gmail.com>
Fully functional proxy model.
Does not track the changes of the "hidden object" property though.
Revert "Fully functional proxy model."

This reverts commit ee83d6464e362d8b5722b10466f084753972f417.