Add an ability to bind actions for clusters

[alexschedrov]

I think it's good feature to be able to bind some actions for clusters, e.g. click.

1. When you have a lot of items in timeline, there's a use case when clusters never expanded.
2. When you want to zoom in on cluster click.

$('.timeline-cluster').once().click(function() {
      var cluster = timeline.getCluster($(this).data('cluster-index'));
      // Do whatever you want with cluster and his timeline items.
      // - you can open dialog with list of items inside clusters.
      // - you can zoom in timeline:
      // links.Timeline.preventDefault(event);
      // links.Timeline.stopPropagation(event);
      // timeline.zoom(0.4);
      // timeline.trigger("rangechange");
      // timeline.trigger("rangechanged");
    });

[josdejong]

Thanks for your PR @Sanchiz . Two details:

• The string 'events </div>'' should be ' events</div>' (space before, and not after the word)
• How about calling the attribute data-cluster-index instead of data-cluster-id to keep all naming consistent?

[alexschedrov]

@josdejong Sounds good! Done

[josdejong]

Thanks. Can you please also fix the first bullet? There is no space before the word events now, so the cluster items would display something like 12events instead of 12 events.

[alexschedrov]

@josdejong oops, fixed. Also I'm going to create another PR and move cluster label into separate configuration.

[josdejong]

awesome, thanks