MND-12: Fix duplicate Disqus IDs

This patch set fixes the generation of duplicate Disqus IDs in the
HTML outputs.

* Quick Start Guides' book element "xml:id"s made unique
* Document version to be included in generated Disqus IDs
* Build script enhanced to detect duplicate Disqus IDs

Change-Id: I3f82db218327ebc8bd0653857d35628ca4749be4
Signed-off-by: Jan Hilberath <jan@midokura.com>
Merge "MND-12: Fix duplicate Disqus IDs"