Rewrites to share more code with samba module
Allowed nested groups sync with OpenLDAP and reused as much as possible code from EBox::Users::Group from EBox::Samba::Group
Improved the way we sync group memberships from Samba to Zentyal so we are able to sync nested groups if they are not yet created at that point
Fixed zentyal group memberships sync with Samba to handle all supported members and to sync on group creation, not just on group update