adding CSRF token to logout in nav

Currently unused, but will need if we re-add it.
shifting admin password validation to lower level
fixed hashing of user passwords

We were checking for self.password instead of password, which meant that
passwords were never getting salted correctly.
adding signup link
adjusting styling of login/signup pages
better display of error messages

Also handled inactive users and cases in which people try to sign in/log
in when they're already authenticated.
adding link to nav bar for admins
locking down admin views