refs #2714 improved csv/tsv export

core/API/DocumentationGenerator.php

core/API/ResponseBuilder.php

core/DataTable/Renderer/Csv.php

core/Translate.php

lang/de.php

lang/en.php

plugins/API/API.php

plugins/CoreHome/templates/datatable.js

tests/integration/Integration.php

tests/integration/Main.test.php

...csvExport_xp0__CustomVariables.getCustomVariables_day.csv

...on/expected/test_csvExport_xp0__VisitsSummary.get_day.csv

...ner0_trans-en__CustomVariables.getCustomVariables_day.csv

..._csvExport_xp1_inner0_trans-en__VisitsSummary.get_day.csv

...ner1_trans-de__CustomVariables.getCustomVariables_day.csv

..._csvExport_xp1_inner1_trans-de__VisitsSummary.get_day.csv