TreeEditor: Add `dragging` CSS class to body when dragging
TreeEditor: Add `dragging` CSS class to body when dragging

mjl/feincms,nickburlett/feincms,michaelkuty/feincms,michaelkuty/feincms,joshuajonah/feincms,feincms/feincms,matthiask/feincms2-content,mjl/feincms,matthiask/feincms2-content,feincms/feincms,pjdelport/feincms,matthiask/django-content-editor,pjdelport/feincms,mjl/feincms,joshuajonah/feincms,nickburlett/feincms,matthiask/feincms2-content,feincms/feincms,matthiask/django-content-editor,matthiask/django-content-editor,nickburlett/feincms,nickburlett/feincms,joshuajonah/feincms,pjdelport/feincms,matthiask/django-content-editor,joshuajonah/feincms,michaelkuty/feincms,michaelkuty/feincms