Doc: Adding a "What's New in Qt 5.2" page

-taken from http://qt-project.org/wiki/New-Features-in-Qt-5.2

Task-number: QTBUG-33596
Change-Id: Ia807efd3454ceea13d771968b6ce1a994f75ea87
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Geir Vattekar <geir.vattekar@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Doc: Adding list of best practices into list of overviews.

-brings better visibility to the best practices

Task-number: QTBUG-33360
Change-Id: I2e6b185b63895a04d67aaf419ab678ccd9a1a02d
Reviewed-by: Geir Vattekar <geir.vattekar@digia.com>