Add support for retrieval of a feature as a feature resource

[jkerr5]

Per this spec https://resources.arcgis.com/en/help/rest/apiref/fsfeature.html clients should be able to request a feature as a resource using a URL like http://<featurelayer-url>/<featureId>

The feature id currently gets passed through to providers as the method but even if the feature is returned by the provider, the result returned from koop is

{"error":"Method not supported"}

Likely need a new route to handle this.

[dmfenton]

On it