Add external connectivity entities that are missing from docs

Commit adds classes:
- ProgramExternalConnectivityEntity
- RevokeExternalConnectivityEntity
in package docker_plugin_api.NetworkDriverEntities

These two are missing from integration docs:
https://github.com/moby/libnetwork/blob/master/docs/remote.md
but are present in implementation:
https://github.com/moby/libnetwork/blob/master/driverapi/driverapi.go