datasets can also be created for experiments, not only samples

src/python/OBis/obis/dm/config.py

src/python/OBis/obis/dm/data_mgmt.py

src/python/OBis/obis/scripts/cli.py

src/python/PyBis/pybis/data_set.py

src/python/PyBis/pybis/pybis.py

src/vagrant/obis/README.md