In the [JS template](https://github.com/mu-semtech/mu-javascript-template/blob/master/helpers/mu/server.js#L30-L35)
errors get a message passed in which is returned as the title member.

Note that the JS template should also pass status as a member of the
error obejct, as happens here, but it currently doesn't.

It seems to make sense to describe the specific model that may be
followed because we had to look it up ourselves.  Updating the
implementation to that.

The error helper now has deprecated support for **kwargs.  Any argument
that does not belong to the runtime will be warned about.