Define login_form contents in fewer places

Move to a template in index.html for defining the contents of
login_form when not actually logged in.

Previously, we had several places where the HTML contents of the
login form were stored, some different than others.

This unifies, while still leaving one "duplicate" set of contents in
place in the actual index.html (not the template).

From what I can see currently, this baseline is always replaced with
the template, and the baseline could be removed in the future.

Signed-off-by: Jeff Godin <jgodin@tadl.org>
Add link to new user registration

Add link in login form to new user registration page.

Signed-off-by: Jeff Godin <jgodin@tadl.org>
Add password reset request UI

Add password reset request UI. Passes the supplied value to the
backend to initiate a password reset request.

Includes handling for maintaining the correct keydown behavior
between "login" and "password reset request" modes of the
login_form.

Signed-off-by: Jeff Godin <jgodin@tadl.org>