Added validation-status utility

Given one or more validation reports, it outputs validation status XML.
Added utility to check for well-formed XML files

Given a fileset, the new step 'check-well-formed' reports which are
well-formed XML, as well as an error report containing errors for
non-existant and non-well-formed files.
Added px:media-type for validation-status ports
added vnd.pipeline.report type to utility output port
Validation utils update

Added @internal attribute to document validation report

If d:location is empty, no "Location" is output in the HTML report.
Metadata generation bug fix

Fixes MODS bug
https://code.google.com/p/daisy-pipeline/issues/detail?id=328
Merged branch check-well-formed. Close #25.