Fix cluster click listeners

Hi,

I wasn't able to have ClusterManager call the OnClusterClickListener and OnClusterItemClickListener callbacks that I attached. This pull request fixes the problem I had.

I patched ClusteringDemoActivity in the demo application to act on the mentioned callbacks for testing, available here:  https://github.com/infinityb/android-maps-utils/tree/demo-with-toasts

Regards,
Stacey Ell