Password reset feature

Uses a seven step procedure:
  1. (user) Fails to login twice or more
  2. Clicks the 'Forgot my password' link on the login form
  3. Submits the username or email address and triggers a password-reset
     email
  4. Clicks the link in the email and is directed back to the reset page
  5. Enters the username or email again and is logged in
  6. Password change is forced, but current password is not required
  7. Password is updated, user can continue the session without
     authenticating again

**Outstanding**
  * ~~SQL edit and migration script to add a default template for the password reset email~~