group: add support for members

members, addusers, delusers, and in pillar examples

pillar.example

   niceguys:
     gid: 4242
     system: False
+    addusers: root
+    delusers: toor
+  ssl-cert:
+    system: True
+    members:
+    - www-data
+    - openldap

users/init.sls

     - name: {{ group }}
     - gid: {{ setting.get('gid') }}
     - system: {{ setting.get('system',"False") }}
+    - members: {{ setting.get('members')|json }}
+    - addusers: {{ setting.get('addusers')|json }}
+    - delusers: {{ setting.get('delusers')|json }}
 {% endif %}
 {% endfor %}