Bug 36102: (follow-up) Add cud-login to the login form

Bug 36102: (follow-up) Add cud-login to the login form

Hum this didn't make sense. We are not checking credentials after
checkauth.

This patch is suggesting to rename "userid" and "password" parameters
from login forms to "login_userid" and "login_password" to not interfere
with other parameters with the same name.

This looks quite correct, however I am seeing
  "The form submission failed (Wrong CSRF token)."
in the log after a successful login. Which feels wrong, what's
happening?

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>