Add stats support, the url is vpn/sites/<id>/stats
Change pri_networks format from string to a list of hash.
For example, the str format of pri_networks is
"192.168.1.0/24,192.168.2.0/24-192.168.11.0/24;192.168.3.0/24-192.168.33.0/24,192.168.44.0/24".
When converted to a list of hash, the format will be like below
'pri_networks' : [
            {
               'local_subnets': "192.168.1.0/24,192.168.2.0/24",
               'peer_subnets': "192.168.11.0/24"
            },{
               'local_subnets': "192.168.3.0/24",
               'peer_subnets': "192.168.33.0/24,192.168.44.0/24"
            }
        ]