REST call of DataAccessObject.findById returns 404

Modify the remoting configuration of `DataAccessObject.findById()` and add a `rest.before` handler that converts `null` to 404 error.

The change is covered by a test in loopback project (see strongloop/loopback#75).

Requires strongloop/strong-remoting#22.

/to: @raymondfeng or @ritch - please review
/cc: @Schoonology FYI

BTW having unit-tests in a different project is a serious code smell. We should either consider moving configuration of remoting options to loopback, or write integration tests that setup a strong-remoting server to test this config.