fix #1762(selection): batch events for batch selection

Add batch selection event to the selection api.  Provide an option
to turn the batch event on and off - so users can just rely on
multiple calls to the individual row event if they wish.  By default
the batch events are used.
Merge pull request #1865 from PaulL1/1762_batch_selection_events

fix #1762(selection): batch events for batch selection