setup.py: mark pvl as a namespace package, as pip install --upgrade will otherwise nuke all other namespaced packages

pvl.ldap.args: use new LDAP_URI/LDAP_BASE/ENCODING defaults, and set LDAPClient(interactive=True) for cli usage

pvl.ldap.domain: use pvl.ldap.connection LDAP_URI/LDAP_BASE defaults, new ENCODING=utf-8 default, and interactive=False default to disable use of getpass prompts

pvl.ldap.connection: get LDAP_BASE default from options, now that recent python-ldap versions support it

pvldap.group: revert GID_MIN/MAX/MONOTONIC defaults to debian standard, use pvl.args.parse to support /etc/pvl/ldap/group.conf