Merge branch 'release/4.0.0'

Jenkinsfile

oaipmh-core/pom.xml

...c/main/java/info/textgrid/middleware/DARIAHConstants.java

...main/java/info/textgrid/middleware/DublinCoreBuilder.java

.../java/info/textgrid/middleware/DublinCoreFieldLoader.java

.../src/main/java/info/textgrid/middleware/ErrorHandler.java

.../textgrid/middleware/IdentifierListDelivererAbstract.java

.../textgrid/middleware/IdentifierListDelivererDATACITE.java

...a/info/textgrid/middleware/IdentifierListDelivererDC.java

...nfo/textgrid/middleware/IdentifierListDelivererIDIOM.java

...textgrid/middleware/IdentifierListDelivererInterface.java

...o/textgrid/middleware/MetadataFormatListDelivererAbs.java

...fo/textgrid/middleware/MetadataFormatListDelivererDH.java

...grid/middleware/MetadataFormatListDelivererInterface.java

...fo/textgrid/middleware/MetadataFormatListDelivererTG.java

...c/main/java/info/textgrid/middleware/OAIPMHConstants.java

...re/src/main/java/info/textgrid/middleware/OAIPMHImpl.java

...rc/main/java/info/textgrid/middleware/OAIPMHProducer.java

...c/main/java/info/textgrid/middleware/OAIPMHUtilities.java

.../src/main/java/info/textgrid/middleware/OAI_ESClient.java