removed superfluous driver registration
Merge pull request #213 from nla/sc-db-driver-fix

removed superfluous driver registration, merged.
Merge remote-tracking branch 'origin/master' into dsc-83
actually add the new derivative when overwriting the old one.
pom and readme
Merge pull request #214 from nla/js-fixDerivativeCreation

actually add the new derivative when overwriting the old one.
Merge remote-tracking branch 'origin/master' into dsc-83
additional field mapping for EAD.