[dataimport] separate entities table from other metadata in SQLGenObjectStore
'entities' needs to be updated first as every other table has references
to its rows. Remove use of thread-local storage in the process.
related to #9177565.
change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')