Improve format of canonicalsv tool for easier upgrade support

To make it easier for viewing and comparing canonicalsv produced output, especially when comparing and diffing xml export for upgrade support,
I'm providing a few tweaks and improvements to the (xml type) output format:

• Drop the empty 'root' node
• Render node names as (optionally fully) qualified paths, so you can easier keep track 'where you are' in a deep/long output, and especially within a patch file
• Add an extra command line parameter to specify the qualified prefix path from where the xml export was generated, so the output will generate fully qualified node paths (see also previous change)
• Drop the '+ ' prefix for node (path) names, as these now start with a / already and thus already are clearly marked, furthermore it reduces confusion when generating a patch file (which adds another '+ ' or '- ' in front of changed lines.