Required container fields check

Some fields were used in context checks, but the fields themselves were
not checked for existence
Conversion tooling from .sch to .xsl
Ignore
BII v2 schematrons
Adjusted for use in SI merge

ID's of the documents were changed otherwise there was a conflict with
the BII ones
Fixed incorrect descendant axis use
Use local saxon
Merged with PEPPOL v2 and BII 2 rules