Added changelog for 5.2.0 release

Task-number: QTBUG-33360
Change-Id: I29a5a21fe213bd7bfff3f4707de6c8142a74afcf
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Doc: Fixed missing links in iOS, Android, WinCE, and Mac OS X pages.

-more attention is given to these pages for 5.2.0, so it is a good
 idea to make sure links work.

-WinCE page removed because it caused missing links.
 Pages do not link to it anyway.

Task-number: QTBUG-33360
Change-Id: I54b7ad874434feeef5670f15351ff522ebfec0b3
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>