[#186] Cluster map markers

* Add maps utils library
* Load items directly into the cluster manager
* Upgrade min version (10)
[#186] Partial update of clusters
[#186] Show total amount of points in the cluster
[#186] Maximize screen bounds for computed points
[#186] Handle LatLng serialization and read
[#186] Extend original LatLngBounds object

* Clean up
[#186] Be nice and add some Javadoc
[#186] Revert version number

* Version upgrades will be handled separately
[#186] Use explicit library version
Merge pull request #212 from akvo/issue/186-clustering

Code checked, (to the extent possible without studying the google play services in detail)