Currently view content is not created until after onContentYChanged
handlers are called, which is not what the user would expect
This change moves the contentX/YChanged emission to
after the content update and also removes the need for a
connect() in Flickable init.

Task-number: QTBUG-23462
Change-Id: I11e87a78160033e3ec6a9e7de733474f8345050d
Reviewed-by: Bea Lam <bea.lam@nokia.com>