Issue #119

Fixes 2 problems associated with #119

1) Trying to create a new tag/sensor without a serial number no longer gives you a Grails error page
2) You can no longer create/update a sensor to a type that conflicts with the other sensors on the tag
Yeah. Despite the fact that it closes the response, the render() method doesn't finish the execution of the method. So if this return wasn't here the rest of the method would execute and we don't want that.