AVISIMPL-204: added missing error message
NOISSUE: disabling edition mods schematron validation
AVISIMPL-163: changed validation of attributes height, width, hpos and
vpos
AVISIMPL-163: added more comments
Merge branch 'master' of github.com:statsbiblioteket/newspaper-batch-metadata-checker
added more test to alto and mix schematron validation