Modernize dumpRDF script

- Fix bug 35679
- General script hygiene
- SMWExportController::printAll is now protected, the public interface
`printAllToOutput` and `printAllToFile` are two dedicated methods to do
only things they are responsible for
- Add `DumpRdfMaintenanceRegressionTest`
- Add `RdfXmlSerializationExportDBIntegrationTest`
Merge pull request #379 from SemanticMediaWiki/rdf-dump

Modernize dumpRDF script