Fix invalid positioning when basket is scrolled

When basket got scrolled down or right itemAt(enent->screenPos()) method treats screenPos() as coordinates from the absolute topleft corner of the view not the scrolled one. So when basket is scrolled and user starts selecting text inside editor note dragging starts instead. This is fixed by taking into account scroll shift
compilation fix
Prevent drag & drop group of notes into itself
merge pull requests #5 and #6