_getGhost = function(event, $draggedItem) {
  // add ghost item & draggedItem to ghost object
  var ghost = _makeGhost($draggedItem);
  // attach ghost position
  ghost = _addGhostPos(event, ghost);
  // attach ghost to dataTransfer
  _attachGhost(event, ghost);
}
_getGhost constructs ghost and attaches it to dataTransfer
@param [event] event - the original drag event object
@param [jQuery selection] $draggedItem - the item that the user drags
@param [object] ghostOpt - the ghost options