Add future departure for NS api

The nederlandse_spoorwegen api is only usable if you have a very strict routine.

Because you only can get the current train. That can already be departed. Or a fixed time.

Adding an future department option that makes amount of sensors with the next trains will make the api much more usable for people that dont live at the minute.

sensor:
  - platform: ovapi
    name: bus 80
    stop_code: hlmvuh
    route_code: 55002200
    show_future_departures: 2

  - platform: nederlandse_spoorwegen
    api_key: ########
    routes:
    - name: Haarlem-Gouda
      from: HLM
      to: GD