Add a QApplication::queryKeyboardModifiers() method.

Add a QApplication::queryKeyboardModifiers() method.

QApplication::keyboardModifiers returns the keyboard modifiers
from the last keypress event in this process, as documented. However
there are use cases for querying keyboard modifiers as they currently are,
see QTBUG-11243.

Merge-request: 585
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@nokia.com>
(cherry picked from commit 3b5354386225974ea6db78c12f32cb81e2d50104)

Change-Id: I9b4e54ac79fc225e3ed8d2bcaba953a6eb59f0d2
Reviewed-on: http://codereview.qt.nokia.com/3581
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@nokia.com>