Doc: Removed extra "\group events" page in Qt GUI.

The group page is in Qt Core already.

Task-number: QTBUG-32580
Change-Id: If9c4b40bad96c138dd8fe98e71378f73269c66e4
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Cocoa: support QWheelEvent::Phase

The started & ended phases are required for implementing correctly
behaving transient scrollbars (ie. they become and stay visible when
touching the pad with two fingers).

Change-Id: I718d991ba6fd7e949cf9790f3bae285000fce576
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>