SSDM-6762: added error log; added -d option to removeref

obis/.gitignore

obis/src/python/integration_tests/integration_tests.py

obis/src/python/obis/dm/command_log.py

obis/src/python/obis/dm/commands/clone.py

obis/src/python/obis/dm/commands/move.py

obis/src/python/obis/dm/commands/openbis_command.py

obis/src/python/obis/dm/commands/removeref.py

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

obis/src/python/obis/dm/repository_utils.py

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