Add basic sign up/log in pages

This adds a sessions controller for logging in/out.  It also adds a users controller to have a sign up page.

Users can now create an account and log in and out.

The pages do not look pretty, but that was not my intention at this point.

Also, I added some tests, but they don't test all of my changes.  I don't think that we need 100% code coverage for this, but I do think it would be good to code some tests every time.