[transaction] explicit Transaction cnxset attribute The Transaction object have a lot more attribute that those previously declared in __init__. They are just dynamically assigned in Session code. This changeset explicit the ``cnxset`` and ``mode`` attribute declaration.

sync_schema_props_perms(('State', 'state_of', 'Workflow'), commit=False)
sync_schema_props_perms(('State', 'name', 'String'))