Enable Simple signup

This is just a very simple user creation addition.
There is now a link on the default page to take you to signup.
I posted my questions throughout the code.

@melari, signup works, but I created this PR mainly to get some feedback.
True, but your browser needs the URL to post to, not the rails controller and method names. So when you call `form_tag(...`, rails does a reverse route lookup to find out that the url corresponding to the `user#create` route is "create_user" and puts that into the generated html form.