Add a 'report' output port to all validation steps

[ndw]

Already supported in p:validate-with-schematron. Add to p:validate-with-relax-ng and p:validate-with-xml-schema.

Define a unified reporting language for validation errors? SVRL for all validation steps?

[xatapult]

See also #397

[xatapult]

The validation steps get an option to switch off the error throw.
They also all get a report port where some report will appear about the error
TThis is either what we decide on in #397 or the current error document. TBD

[ndw]

Done