Doc: Get Creator and Extending manuals to use new qdocconf variables.

-navigation variables for Qt 5.2's navigation bar
-buildversion is for including specific build information such
 as branch name and patch version

Change-Id: I4d36f1ea73b8c37ab787d154c9fdd91650305bc5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>