genius.utils.batching.ActionableResource is inefficient

ActionableResource has a number of deficiencies:

• the interface seems to be mutable, where in fact is really is not
• each resource requires a key, which is only ever used impossible cases – and it forces clients to come up with Strings. Users resort to inefficient use to toString() on various objects, mostly InstanceIdentifier
• the interface hides really four distinct polymorphic cases, each of which should be tightly encapsulated

Rework the interface so it addresses all these concerns.