Add page documenting how to use xsd-fu

Largely copied from http://trac.openmicroscopy.org.uk/ome/wiki/XsdFu

Fixes #2228.
Style fixes for the xsd-fu page
Fix indenting as required by Plone
Merge pull request #598 from melissalinkert/xsd-fu-doc

Add page documenting how to use xsd-fu