extend policy rules to have name attribute in api

It would be nice if policy_rules also had a name attribute. For example adding --name port_security_group to the following command:

 openstack congress policy rule create classification --name port_security_group "port_security_group(port, security_group_name) :-neutron:ports(addr_pairs, security_groups, extra_dhcp_opts, binding_cap, status, name, admin_state_up, network_id, tenant_id, binding_vif, device_owner, mac_address, fixed_ips, port, device_id, binding_host_id1), neutron:ports.security_groups(security_groups, security_group_id), neutron:security_groups(tenant_id2, security_group_name, desc2, security_group_id)"

Add name here:
https://github.com/stackforge/congress/blob/master/congress/api/rule_model.py#L86

Extend db code to save name and generate migration:
https://github.com/stackforge/congress/blob/master/congress/db/db_policy_rules.py#L30
name = sa.Column(sa.String(255)

We'll also then need to update the python-congressclient to expose this name attribute and allow people to delete by name.