Provide a mechanism of testing the SDK locally without need for the snet platform

[raamb]

Ok, after porting one of my grpc clients to this sdk (or the simple alternative) there is one major design thing I'm concerned about.

It looks like I need different code paths for singularitynet and for calling the service without the singularitynet layer. e.g. if I have a local service, and I'm testing it (without any blockchain stuff), I want to use almost the exact same code as when I'm calling the production service.

Ideally I'd be able to fetch the model from either a local directory (yet to be published), or from snet. Then it'd be compiled and I could create a stub and request, but it'd only add the MPE stuff if I'm actually calling the service via MPE.

Any idea if you've already allowed for this @vforvalerio87 - or if it'd be easy to support something like this?

snet = Snet(private_key=pk)
if snet_enabled:
    client = snet.client("snet", "face-detect")
else:
    client = snet.client(directory="service/service_spec", endpoint="http://localhost:50015")

### snet-sdk-python with full grpc specification
stub = client.grpc.face_detect_pb2_grpc.FaceDetectStub(client.grpc_channel)
request = client.grpc.face_detect_pb2.Request(image=client.grpc.face_detect_pb2.ImageRGB(content=...))
faces = stub.FindFace(request)

### simple-sdk version
stub = client.get_stub()
request_cls = client.get_request(method='FindFace')
request = request_cls(image={content=...}))
rez = stub.FindFace(request)

If a directory and endpoint is provided, then no MPE work is done, nothing is looked up on the registry etc.

Edit: updated to include what @astroseger's simple-sdk would have to look like.

Originally posted by @ferrouswheel in #5 (comment)