add: MergedColumnDataReportingPlugin for column-based merging of TSV files

...rver/plugins/demo/AbstractDataMergingReportingPlugin.java

...rver/plugins/demo/DatasetModificationReportingPlugin.java

.../dss/generic/server/plugins/demo/DemoReportingPlugin.java

.../server/plugins/demo/MergedColumnDataReportingPlugin.java

...eneric/server/plugins/demo/MergedDataReportingPlugin.java

...ric/server/plugins/demo/MergedRowDataReportingPlugin.java

...is/dss/generic/server/plugins/tasks/DatasetFileLines.java

...eric/server/plugins/tasks/IterativeTableModelBuilder.java

...generic/server/plugins/tasks/SimpleTableModelBuilder.java

.../server/plugins/tasks/IterativeTableModelBuilderTest.java