Remove Terraformer dependency, Remove submodules

This PR removes Esri Leaflets dependency on Terraformer by porting in https://github.com/Esri/terraformer-arcgis-parser and adapting it to work without Terraformer. The dependency on https://github.com/Esri/terraformer-geostore-rtree was removed by replacing it with https://github.com/mourner/rbush. Overall this saves about 17k from the minified filesize.

This also changes the test suite to work with the CDN version of Leaflet and removed the submodules for Terraformer and Leaflet.