Bug 26828: Set focus for cursor to current password field when updating in the OPAC

Bug 26828: Set focus for cursor to current password field when updating in the OPAC

This patch adds the "focus" class to the first field in the
OPAC's password update form so that the field automatically receives
focus upon page load.

To test, apply the patch and make sure the OpacPasswordChange system
preference is enabled.

- Log in to the OPAC
- Open the "Change your password" page
- The cursor should automatically be in the "Current password" field
  when the page loads.

Signed-off-by: B Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>