Add more input validation

We're not on the same page for the reason for these security validations.

It would be nice if every time someone hit this route, it came through the application. The application as we have designed it will never make the request without an ownerName. However, the route can in fact be hit by anything. As the app stands, a request without any fields at all will totally crash Repcoin. We can't assume that there is a req.body.ownerName.