[transaction] handle ``mode`` default value in Transaction
The transaction mode is now explicitly passed at creation time and always read
from the Transaction object.
Note that there is a slight behavior change. The transaction mode is now set at
the creation of the transaction. Changes made to the default value have no
longer any effect on existing transaction.
from cubicweb.schemas.base import in_group, CWSourceSchemaConfig
# copy __permissions__ to avoid modifying a shared dictionary
in_group.__permissions__ = in_group.__permissions__.copy()
in_group.__permissions__['read'] = ('managers',)
cw_for_source = CWSourceSchemaConfig.get_relation('cw_for_source')
cw_for_source.__permissions__ = {'read': ('managers', 'users'),
'add': ('managers',),
'delete': ('managers',)}