TransformationWorkspace: support custom transformation targets

Change-Id: I816f0fd6a37ba53dd4799803dfd11e3dc44e301a
Reviewed-on: http://gerrit.esdi-community.eu/3562
Tested-by: Jenkins <sitemple@igd.fraunhofer.de>
Reviewed-by: Simon Templer <simon.templer@igd.fraunhofer.de>