PodioInput does not limit the collections that are read

[tmadlener]

The collections options of the PodioInput does not work as intended, I think. It reads the complete Frame, i.e. all collections, but then effectively just gives access to the ones that are specified (even others would be available). More importantly, in combination with PodioOutput all collections that are available on file will be written to the outputfile as well, which is quite unexpected IMHO.