Add change log for Qt 5.4.0 release

Change-Id: I9eca03f01ba01e9952c28c6d4bd14f656aa5d838
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Timur Pocheptsov <Timur.Pocheptsov@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>