Add support for clustering

[allisonmuise]

Clustering can be set on a layer in the web map by clicking the three dots after the layer name and choosing 'Clustering'

The features should render the same in the map viewer and the application. The table should still list each individual feature and the details panel should display the layer popup (not the cluster popup)

I will send example map and app urls via email. To include this in 5.3, I will need a code drop by next Wednesday (Sept 13)

[allisonmuise]

Reporter cannot currently support clustering. We will wait on adding support to Manager until Reporter supports it as well.