Define a new Model method "createOptionsFromRemotingContext" that allows
models to define what "options" should be passed to methods invoked
via strong-remoting (e.g. REST).
Define a new http mapping `http: 'optionsFromRequest'` that invokes
`Model.createOptionsFromRemotingContext` to build the value from
remoting context.
This should provide enough infrastructure for components and
applications to implement their own ways of building the "options"
object.