Add changelog for upcoming Qt 5.3.1 release

Change-Id: I0f709d1066763d2c17950da8b092ecf5f28d9556
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Reviewed-by: Sergio Ahumada <sahumada@blackberry.com>