Add remoting options to server/config.json

/to @bajtos @ritch 

See https://github.com/strongloop/loopback/issues/608
See https://github.com/strongloop/loopback/pull/337
Yes, that will be the best.

Here are some alternatives:
 - Change the value of `supportedTypes` to list all types including xml types. I find that a bit confusing, plus it is difficult to upgrade. You have to upgrade your config file if you want to use a new JSON-based type like `application/vnd.api+json`.

- Keep the current value,  tell people to delete `supportedTypes` together with changing `xml:true`. However, the problem with upgrades is still present.