[IMPR] Allow family files in base_dir by default
[IMPR] Allow family files in base_dir by default

private family files can be registered via register_families_folder()
function already. Register 'families' folder in basedir by default
within config.py.

Change-Id: Ic84fbc6b95910b9b144faa8309c54f3ed3714a11

wikimedia/pywikibot-core,wikimedia/pywikibot-core