More consistent dock widget painting on Windows

More consistent dock widget painting on Windows

Before we would draw dock widget handles on windows classic
and no handles on XP, Vista and Windows 8. This would make it
very hard to make a consistent look and feel across those styles.

I also added a workaround to avoid the redundant toolbar borders
when they are used outside of the toolbar areas.

Change-Id: Ib703453677fcac8d51b2180abe45527297af0a80
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>