DragAndDropTrigger and DragAndDropDirection

Since 1.8.2, you can now choose if you want to begin the drag and drop with a Pan gesture or a LongPress.

• DragAndDropTrigger="Pan"
• DragAndDropTrigger="LongTap"

You can also restrict the drag movement to a given direction:

• For the horizontal layout: DragAndDropDirection = HorizontalOnly
• For the vertical layout: DragAndDropDirection = VerticalOnly

It will give a better more precise drag experience, more precise.

Fixes:

• #27: DragAndDropInfo provides incorrect information for moved item
• #26: ItemsSource does not notice changes to underlying ObservableCollection