transformation CLI: support multiple sources

Change-Id: Ic9b97fbdcb7f2e2b6a03bd384dc9f6940168e850
Reviewed-on: http://gerrit.esdi-community.eu/3197
Tested-by: Jenkins <sitemple@igd.fraunhofer.de>
Reviewed-by: Simon Templer <simon.templer@igd.fraunhofer.de>