Cleans up some views

I noticed a few things with some views/controller actions that I though we should change. Not crucially important but I figured I would fix them now and not leave them for later.

* The new event page had a duplicate form so I removed the old one
* The route for unsuccessful registration ended in redirecting to '/', not rendering the registration page as intended, which I changed by adding "return" before the render
* Changed the error message after unsuccessful login to say "Invalid email address or password" instead of saying which one. Initially I had a bigger error after unsuccessful login but it was a problem with another branch being behind, so I only changed the error message.