Handle result image layers generically wherever applicable.
Clean up GeoprocessingWidget#extractLargestResultLayerExtent().

* Remove unused token in result images request logic.

* Update pending result layers to process when result image request fails.

* Rename pending result layers count variable.
Handle 10.1+ result map services.
Clean up.
Merge branch '#77/update-gp-to-handle-10.1-result-map-services' into develop