Changes to user/site interaction

Several changes to urls/views. The default page loaded is now the
index. Login views have been condensed into a single view which
redirects to the home page on login. All views which require
authentication have been marked with the login_required decorator.
Creator the logout_required decorator to restrict access to
authenticated users where appropriate (they should not be able to
access the login page, etc.)
Changed the default login url in settings.py