NEW Support for other authenticators

I've added the ability to add other authenticators to the RestfulServer

Use the config system to change the authenticator option and it'll call
`authenticate` on that class.

I've assumed that one won't need any parameters sent to that and
everything can be taken from `Controller::curr()->request`

This relies on the default authenticator being able to accept the
standard email/password identifiers. I imagine anyone using a default
authenticator to that will go to the trouble of adding a RestfulServer
authenticator too.