SSDM-6427: using git annex hash as checksum (set to MD5); bugfixes

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

src/python/OBis/obis/dm/commands/openbis_sync.py

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

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

src/python/OBis/obis/dm/git-annex-attributes

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

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

src/python/PyBis/pybis/data_set.py