ItemSwipeActionCompleteContex missing from docs

[LanceMcCarthy]

In the ListView Gestures documentation:
http://docs.telerik.com/windows-universal/controls/radlistview/features/listview-gestures

We provide erroneous information about how to implement SwipeAction. For example, there is no longer a "ItemDragCompleteContext" or a property named "SourceType"

There is also no mention of how to use ItemDragCompleteContext or ItemActionTapContext.

We should add a section on how to implement the SwipeAction and how to detect which action was pressed.