add interaction toggle example

Do we support calling `interaction` multiple times for a given interaction? E.g.

```js
goDecorate.interaction(interaction, map1);
goDecorate.interaction(interaction, map2);
```

In that case we should have something like this:

```js
  interaction: function(interaction, map) {
    goog.asserts.assertInstanceof(interaction, ol.interaction.Interaction);
    var previousMap = interaction.getMap();
    if (previousMap !== null) {
        previousMap.removeInteraction(interaction);
    }
    // …
  }
```