Provide support for JSON config

[ddobric]

In StartServiceHostAsync(...)

        if (searchPattern.ToLower().EndsWith(".xml"))
                        microServices = LoadServicesFromXml(configFiles, knownTypes);
                    else
                        throw new NotSupportedException("JSON not yet supported!");
                      **TODO**
                    //instances = `LoadServicesFromJson`(configFiles, knownTypes, out microServices);