feat: add selection to/in datatable

[samsp-msft]

🙋 Feature Request

DataTable should include row selection support

🤔 Expected Behavior

It should have a SelectedRowItem and SelectedRowIndex properties, and a SelectionChanged Event.

Selecting a row should set those properties, and fire the event. Similarly if the selection is removed, then fire the event and set the properties to null.

😯 Current Behavior

Remove the amount of code needed by the application.

[LuohuaRain]

#173