REST Pass-through API

The resource-type-registry service allows easy registration of load, list and actions for a resource type. Often, these are simple API calls to a service that need not additional translation. For these cases, this service allows the client easy access to the services without the need to enable additional CORS support.

The proposal is NOT to eliminate all uses of server-side APIs, but rather, ALLOW client code to quickly and easily reach services, taking advantage of a Horizon proxy, without needing to wrestle with CORS enablement in the individual service.

My experience with Designate convinced me that a pass-through API greatly lowers the barrier to entry for contributors and extensions. Combined with the hz-resource-panel, standardized actions, and schema Form, writing a new panel can now move very quickly.

I'm not suggesting we *eliminate* all REST APIs in Horizon...when they are useful, they are a great resource. When they are overhead, let's not require them.