Add location header to REST response...

...after creating a new object.

This fixes https://github.com/projectwonder/wonder/issues/216

When using any ERXRouteController.create(…) method or calling ERXRouteController.registerCreatedObject(…) the REST response will get a location header pointing to the URL to show the newly created object. As default the showAction will be used for that unless another action name was set via setLocationActionName.