Issue #83: Make portal-item-icon utility more reusable.
Issue #83: Assign existing basemap icon when converting from web map.
Issue #83: Split up logic that handles basemap layer icon assignment.
Clean up.

* Add missing semicolons.

* Rename variable.

* Remove unused variables.
Change IconFetchEvent.COMPLETE value to camel case.
Merge branch '#83/assign-existing-basemap-icon-when-converting-from-web-map' into develop