Update for Runtime v100.0

[nixta]

Clustering is not yet available in the new Runtime v100.

Update this plugin to work with Runtime v100

• Investigate performance of using AGSFeatureCollectionTable with AGSFeatureLayer. Update: Performance is good. Going ahead with implementation.

Tasks:

• Implement clustering engine.
• Implement cluster representation.
• Bring work into v.next branch.
• Implement unclustered feature representation.
• Generically handle any spatial reference.
• Calculate grid cell sizes properly.