Signup page more functional.

modified:   app2/forms.py
    Changed password and validate-password fields to wtforms PasswordField().
    Added validators
        email field should be a valid email address.
        password should match validate-password.

modified:   app2/models.py
    Rearranged a comment.

modified:   app2/templates/index.html
    Took out some visible leftovers.
    Put in links for Log in and Sign up.

modified:   app2/templates/signup.html
    Set up so that if "student" or "alumni" is already checked,
    show the related set of prefs when the form is loaded.
    Took out a redundant macro.
    Took out an extra "-->" that was showing.

modified:   app2/views.py
    Cleaned up the code a little, took out debug prints.
    Pass whether "student" or "alumni" is already checked to signup.html.