[ChangeLog][QtQuick] Added Text::linkAt(x,y) method.

Task-number: QTBUG-18946
Change-Id: I3b4071c6117ac0ee636f2fdbd2c392eb05b02dd7
Reviewed-by: Martin Jones <martin.jones@jollamobile.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Alan Alpert <aalpert@blackberry.com>