[multi-sources-removal] Turn ConnectionsSet into simpler ConnectionWrapper also, SqliteConnectionWrapper becomes a subclass. This is allowed since now ConnectionsSet responsability has been reduced to handling the system source only. This changeset also: * drops useless cnxset_set / check_connection api * deprecates former .source / .connection / container api but it renames neither the session's cnxset attribute, nor the related repository method. Related to #2919300

from datetime import datetime

for rtype in ('cw_support', 'cw_dont_cross', 'cw_may_cross'):
    drop_relation_type(rtype)

add_entity_type('CWSourceSchemaConfig')

if not 'url' in schema['CWSource'].subjrels:
    add_attribute('CWSource', 'url')
    add_attribute('CWSource', 'parser')
    add_attribute('CWSource', 'latest_retrieval')