Doc: Modularized Qt XML Patterns documentation.

-moved snippets, images, documentation to src/xmlpatterns
-fixed \snippet tag
-ported module information from qtdoc repository
-enabled "make docs" for the module
-set up qdocconf file and .index file
-updated tests/auto/patternistexamples to point to the new
 snippet locations

Change-Id: Ifd10733c277c6dbacac42898c8e7bacd00d23f27
Reviewed-by: Lars Knoll <lars.knoll@digia.com>