[multi-sources-removal] Simplify ConnectionsSet internal structures and public methods
since it now handles a connection to the system source only
Related to #2919300
[jcr: adjust 3.17.11 migration, fix a number of bugs in new
ConnectionsSet implementation, fix
source.{open,close}_source_connections]
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',)}