Drill down feature in MapViewer

Summary

Ability to show more granularity maps on clicking on geojson layers.

Usage

      drilldown: {
        rootLayer: 'indiaGeojson',
        drilldown_levels: ['STATE_N', 'DISTRICT', 'VILL'],
        nextLayer: function(name) {
          return {
            layerName: name + '_layer',
            layerOptions: {
              url: name + '.geojson',
              type: 'geojson',
              attrs: {
                fillColor: {
                  metric: 'TOT_P',
                  range: 'RdYlGn'
                }
              }
            }
          }
        }
      }

Examples

(Add code samples of usage, with expected output)