Replacing :actor, :curation_concern with config

Instead of requiring the more archaic `register :actor` and `register
:curation_concern` replace with a class attribute that defines the
`curation_concern_type` and derives the parameter hash key from the
`curation_concern_type`.

Provide a shared example in which we can begin extracting default
behavior of a controller.
Merge pull request #81 from ndlib/replacing-controller-actor-curation_concern-with-class-attribute

Replacing :actor, :curation_concern with config