KOP-2139 KOP-2461 XtaFile: Use DataHandler instead of byte[]

src/main/java/de/ozgcloud/xta/client/XtaClient.java

...ava/de/ozgcloud/xta/client/core/WebServiceTypeMapper.java

...n/java/de/ozgcloud/xta/client/core/WrappedXtaService.java

src/main/java/de/ozgcloud/xta/client/model/Identifier.java

src/main/java/de/ozgcloud/xta/client/model/XtaFile.java

src/main/java/de/ozgcloud/xta/client/model/XtaMessage.java

...va/de/ozgcloud/xta/client/XtaClientConfigTestFactory.java

...de/ozgcloud/xta/client/core/WebServiceTypeMapperTest.java

...va/de/ozgcloud/xta/client/core/WrappedXtaServiceTest.java

...java/de/ozgcloud/xta/client/model/XtaFileTestFactory.java

...cloud/xta/client/model/XtaMessageMetaDataTestFactory.java

...a/de/ozgcloud/xta/client/model/XtaMessageTestFactory.java