Adapted ListSets to ES6 and repair noRecordsMatch in ListRecords

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

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

...main/java/info/textgrid/middleware/RecordDelivererDC.java

...info/textgrid/middleware/RecordListDelivererAbstract.java

.../java/info/textgrid/middleware/RecordListDelivererDC.java

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

...re/src/test/java/info/textgrid/middleware/OaiPmhTest.java