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
This is not great. It means that to enable `xml`, you have to edit both `xml` and `supportedTypes` now.

Before this PR, it was enough to add `xml:true` and developers did not need to worry about content types.