Improved transitions for Row, Column, Grid, Flow

The view transitions functionality for ListView and GridView has been
integrated into the positioner elements. Not all of this
functionality is available for positioners, though, since they don't
have models (and thus cannot identify certain model operations) and
they don't manage the lifetime of their children.

Task-number: QTBUG-24336

Change-Id: I71588de289555d2ef5a763af11358bc0af7b31a7
Reviewed-by: Alan Alpert <alan.alpert@nokia.com>