Merge branch 'feature/elastic6' into es6_fumax

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

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

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

...textgrid/middleware/IdentifierListDelivererInterface.java

...info/textgrid/middleware/MetadataFormatListDeliverer.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

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

...java/info/textgrid/middleware/OpenAireIdentifierList.java

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

...ain/java/info/textgrid/middleware/OpenAireRecordList.java

...ava/info/textgrid/middleware/RecordDelivererAbstract.java