Screen-Space Effects Sample: Swapping IModels keeps effects

[dustinlebsock]

When swapping imodels in the screen-space effects samples, all the effects that were ticked are kept, except lens angle. Ideally, the screen effects would be reset.

The ScreenSpace effects are not being cleaned up.

 if (!ScreenSpaceEffectsApi._effectsRegistered) {`
      ScreenSpaceEffectsApi.registerEffects();
      ScreenSpaceEffectsApi._effectsRegistered = true;
}