Add a change password interface

[irl]

Keycloak doesn't seem to provide an easy UI for users to change their own passwords. An admin can add the "update password" required action to force a password change on next login, or users can reset their passwords with the forgotten password flow. A solution to this is:

Knowing that:

• Hackhub knows the username of the logged in user
• User passwords come from LDAP
• 389ds (the LDAP server) supports LDAP password changes

Hackhub can be extended with a password change page:

1. Hackhub asks for the current password and the new password
2. LDAP bind with the username and current password to ldaps://ldap.57north.org.uk/
3. Do the change password over LDAP
4. Forget all the password details as Hackhub has no need for them