[application/connect] simplify connection logic ``application.connect`` now either sets a full featured ``DBAPISession`` to the ``WebRequest`` object or raises ``AuthenticationError``. The creation and usage of a fake DBAPISession is now handled by ``main_handle_request`` when needed. This means that fake DBAPISession are no longer tracked by the session manager and that user are not given anyway to retrieve them for a later request. This fake DBAPISession is still passed to ``core_handle`` because multiple cubes like registration or forgotten password need this behavior. We would like to get ride of it in the future. This clarification of the connection API greatly simplifies ``DBAPISession`` retrieval//creation process opening the way to improvements in this area. Related to #2503918

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',)}