[session] drop useless getter and setter for security Those function have very few user and does not anything fancy. Internal user now access tx.read/write_security directly. External user have been blessed with a writable property. They are only interested in the write part of they did not used the return of the removed function. They access it through the session since I prefer the external world to not be aware of Transaction yet.

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')